Science topic

Chemical Kinetics - Science topic

Prediction, assessments and studies on the composition of reaction mixtures as a function of time, to understand the processes that occur during a reaction, and to identify what controls its rate.
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How to optimize number of theoretical stages in reactive, rectifying and stripping section using sensitivity analysis tool in ASPEN Plus? what would be the independent variable and dependent variable? Kindly explain i am performing simulations on reactive distillation process.
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Hello Abdul,
From my experience, because I also work on reactive distillation processes for CCS, you should take notice of a couple of things.
When using rate-based and packed column type, the number of stages is “virtual” and represents the number of calculations. Anything below 10 is too approximate and anything over 20 doesn’t improve the accuracy and adds extra calculation load and time to the process. Typically, the two columns are packed columns, chosen over the plate ones because the packing can provide a higher contact area between the gaseous and the liquid phase and ensures less pressure drop. [1,2]
If you opt for trays, it is essential to check the column profiles, especially temperature profiles, to observe how they work and if they work correctly. You don't want to see any plateaus in the graphs because reactive distillation operations involve highly exothermic reactions.
There is a great e-book that has a capture on reactive distillation for CC by McGraw-Hill called "Learn Aspen in 24 hours" (LOL).
Hope I helped!
[1]: Plaza, J. M.; Wagener, D. Van; Rochelle, G. T. Modeling CO2 Capture with Aqueous Monoethanolamine. Energy Procedia 2009, 1 (1), 1171–1178. https://doi.org/10.1016/j.egypro.2009.01.154
[2]: Madeddu, C.; Errico, M.; Baratti, R. CO2 Capture by Reactive Absorption Stripping Modeling, Analysis and Design; Springer, 2019. https://doi.org/10.1007/978-3-030-04579-1
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Can we calculate radical contribution using initial reaction rates instead of rate constants in UV/oxidant systems, particularly if the reaction shows unusual behavior at high concentrations of organic matter, affecting the rate constants?
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I might help you if you provide the details. You can message to me.
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Hey Everyone I am looking model free Kinetics calculation sample or tutorial. Also I am looking NLN ( advanced Model free method ) Tutorial ?
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Some time ago i have developed THINKS thermokinetic app, it's free and open-source, available at http://chemphys.space/thinks
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hello Everyone,
if I want to study, coal combustion in different atmospheres for example in O2/N2 and O2/CO2. I obtain the kinetics of both atmospheres using Hetrogenous models. ( Shrinking core model ) and Random pore model.
I was wondering if it’s possible in CFD to study particle profile. Does the heat transfer affect in CFD will calculated based on the Gas composition input or I should add something in UDF file.
FYI, the reaction models are based on conversion so I am not really sure how CFD will identify the differences in Atmospheres.
further, I wish If I found a sample UDF file that been used for Hetrogensous models.
Ahmad
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In general, yes, CFD computations can include particle profiles. The most direct and possibly accurate sources are likely the vendors of the major CFD systems themselves. They may have useful models already, or be willing to help you set up your system, or even take it on for development if they don't have it already in their portfolio of applications.
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Hello! High school work requires some simple chemical kinetics for octane or gasoline combustion (for simple 0D ICE model in COMSOL). Kinetics must contain k and E0 values or reaction rates formulas like R=k*exp(E0/RT). I was looking for simple kinetics, but the simplest models included about 50 reactions. It's too difficult for school level. Does anyone know similar models with 1 or at least no more than 10 reactions?
Thanks for answers.
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The combustion of organics is an extremely complex process and can't be simplified to 10 reaction. This is not for high school level project.
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I am attempting to analyze the significance of minor species within the framework of supersonic combustion inside a model combustor. Your insights on this topic would be greatly appreciated.
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In the H2-O2 combustion system, the HO2 radical plays several significant roles:
  1. Chain Branching: HO2 radicals contribute to radical chain branching reactions, influencing the overall reaction kinetics in combustion systems [5].
  2. Intermediate Species: HO2 radicals serve as intermediate species in various reactions, leading to the formation of important compounds such as hydrogen peroxide (H2O2) through termination steps [4].
  3. Reaction Kinetics: HO2 radicals are involved in reactions with other radicals and species, affecting the combustion kinetics and the overall efficiency of the combustion process [3].
  4. Flame Chemistry: Understanding the presence and behavior of HO2 radicals helps in elucidating flame chemistry, aiding in the design and optimization of combustion systems [2].
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Presently computer science well applicable in various fields of science and many other fields. how best use in chemistry. .
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Computer science has made significant contributions to the field of chemistry, enabling researchers to model complex molecular systems, predict chemical reactions, and analyze vast datasets. Here are some notable applications of computer science in chemistry:
1. **Monte-Carlo Simulations**: These are used in various areas, including environmental and chemistry fields. Monte-Carlo simulations can help in understanding complex chemical systems by using random variables and state-of-art techniques. [Link to the study](https://doi.org/10.54097/hset.v17i.2430)
2. **Molecular Docking and Dynamics**: Computational methods have been developed to solve the molecular docking problem, which is crucial for understanding molecular interactions and designing drugs. [Link to the study](https://doi.org/10.55522/jmpas.v12i1.4137)
3. **Material Science and Molecular Design**: The combination of material science and computer science has shifted the approach from "how to make a molecule" to "what molecule to make." This involves designing new ligands and complexing them with metals like Ruthenium to develop new materials with diverse applications. [Link to the study](https://doi.org/10.33696/pharmacol.4.042)
4. **Simulation of Practical Works of Crystallography**: Technological innovations have led to the development of computer applications that simulate chemical experiments, especially in the field of crystallography. This allows students and researchers to understand and study different crystalline structures using computer-based virtual experiments. [Link to the study](https://doi.org/10.35940/ijrte.c4665.098319)
5. **Computer-assisted Structure Elucidation (CASE)**: CASE systems have been developed to help in the structure elucidation of natural products using spectroscopic data. These systems mimic the expert's way of thinking during the process of structure elucidation. [Link to the study](https://doi.org/10.1039/9781849735186-00187)
6. **Visualization of Proteins**: Modern biochemists use computational methods to visualize proteins, find ligand binding sites, and understand the three-dimensional interactions with coordinated amino acid residues. [Link to the study](https://dblp.org/rec/journals/cse/PineP20)
7. **Nanoscience and Advanced Computational Methods**: Computational methods have been employed to study and design new compounds at the atomic level, leading to the development of software for targeted simulations. [Link to the study](https://doi.org/10.4018/978-1-4666-1607-3)
8. **Quantum Algorithms for Quantum Chemistry**: Quantum algorithms have been developed for ground-state, dynamics, and thermal-state simulation in quantum chemistry, providing a new dimension to the study of molecular systems. [Link to the study](https://arxiv.org/pdf/2001.03685)
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Dear Researchers,
I'm currently working with Dimethyl Disulphide (DMDS) in my research project, and I need to ascertain it's purity. The substance I have is reported to be approximately 99.5% pure on a weight basis.
I am seeking guidance on the best techniques or methods to confirm this level of purity. Are there any industry standard or academic lab procedures that I can use? Are there specific pieces of lab equipment that you would recommend?
I appreciate any advice or resources you can provide.
Best regards,
Amir Darban Loghmani
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you need to have a combination of FTIR, NMR and Mass Spectroscopy. Although any of them can confirm the purity however if possible go for minimum two of them.
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how to define proximate and ultimate analysis in eulerian approach for biomass gasification in fluidized bed?
coal calculator is off and i am using species transport in fluent
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Hello Reza Karimi Ahmadi .. I am trying to solve a similar problem as yours in ANSYS FLUENT. Did you find the solution to this problem. It would be a great help if you could share it with me.
Regards
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Hi, I would appreciate it if you could explain to me which equation is correct for the second-order reaction. In the most textbooks I see "K" instead of "2K" in the equation. Please also see the attached pictures.
Regards,
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R = K[A][B]
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These types of figures are required in reaction kinetics modeling work.
#figure
#plot
#Histogram
#reaction_kinetics
#chemical_kinetics
#combustion
#combustion_kinetics
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Elbatoul Benidris please check your inbox
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I wanted to know if there is such a possibility since I have observed quite little difference in qcal values in case of both PFO and PSO models.
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Yes,it can
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Hello everyone. I need help from you because I need to develop a Pareto Chart applied in chemical kinetics through Minitab. Can you help me with this, please
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Pareto Chart is a normal plot originally plotted from your data obtained. The standardized effects of the chemical kinetics process will be compared to showcase which process parameters that singly or interactively assisted the process.
See minitab tutorial pdf.
Hope it is helpful. Good luck
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Hi everybody. I have a question about study kinetics. So, I did electrolysis by dissolving organic compounds with aquades as a sample under acidic conditions with Na2SO4 as electrolyte, with additional H2O2 (Fenton reaction) using iron as anode and graphite as cathode. In discussing the study of kinetics, I found that if the kinetic graph that R2 close to one or almost linear is in pseudo-second order graph, what does this pseudo-second order mean? what does pseudo-second order actually mean? i was told that "the pseudo explains that something is involved but doesn't appear in the rate law, for example the solvent or there is usually the fraction of the reactant that matters" is that true? So, if what is meant by second order is that there are two reagents that have an effect in this case, for example H2O2 and Na2SO4, but in pseudo-second order something is involved but it doesn't appear, what is it? also, if you also know, what kind of reaction mechanism that produces the pseudo?
Thanks in advance
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Send your email address to me, dgamble@ns.sympatico.ca. I can send my published comments about second order kinetics.
Best regards,
Donald Gamble
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Can absorption isotherms be used for gas-liquid absorption processes?
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In fact, it is actually a bit unusual that with regard to gas-liquid absorption, no names of scholars have been assigned to particular equilibrium curves and their corresponding mathematical functions, other than William Henry.
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Hello,
I have calculated the equilibrium products of high-temperature gaseous reactions from thermodynamic calculations. Meanwhile, I am curious about determining the kinetics of those reactions. I checked various resources, however cannot find any information on the kinetics of the reactions given below:
CO2 <--> CO + O2
2CO <--> C + CO2
CO2 + CH4 <--> 2CO + 2H2
CH4 <--> C + 2H2
Can you please provide me the procedure or references where I can estimate the kinetics of those reactions? Many thanks!
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While the chemical equilibrium is strictly dictated by thermodynamics, the kinetics expressions depend on the type of catalyst (these reactions are usually catalysed) and may vary from one another. Some typical expressions can be found in Chemical Engineering Journal (2007), 134(1–3), 138–144. https://doi.org/10.1016/j.cej.2007.03.051
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I am trying to simulate methane combustion in an industrial high-pressure gas turbine combustor using the species transport model in fluent with detailed GRI mech 3 mechanism but I get no combustion. I also patch the temperature to a high value.
Has anyone worked with Detailed methane-air combustion in Ansys Fluent?
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The study of combustion is important to optimize the design and operating parameters of a combustor. The combustion between the fuel and air involves the conversion of the chemical energy of the species to heat energy. Complete combustion is desirable to get the maximum thermal efficiency out of it. Incomplete combustion is not desirable as it emits hazardous unburnt hydrocarbon as well as CO2, NOx, etc to the environment.
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Mentioned in the publication ''RANS simulations on combustion and emission characteristics of a premixed NH3/H2 swirling flame with reduced chemical kinetic mode''.
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I think you might mean DRM 19 CHEMKIN files.
You can download it by googling it.
If you cannot find it, give me your email address, and I'll send it to you.
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See scenario below:
You are monitoring a certain chemical reaction (browning) of a product stored at different temperatures over a certain period. When applying kinetics to determine the reaction order, sometimes you find that this reaction fits/obeys both reaction orders (zero- and first-order). When determining the activation energy using the Arrhenius equation ( ln k = ln A - Ea/RT), which rate constants (k) do you choose (zero - k0 or first - k1)? Can you apply both or is it always k0?
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Toyese Oyegoke, Of course, browning, presumably food, is not an elementary reaction. There we can deal with the oxidation of various food components, enzymatic reactions and a slow loss of water. Structural and texture changes may also occur. One can, obviously, try to describe the kinetic curves (degree of browning vs. time) with known functions and on this basis infer the order of the process (treated as a single step), but one need to have reliable data. But if the changes in the degree of browning are small, as the author of the question writes, such calculations will be unreliable. And one more thing. In such a situation, the use of the term apparent activation energy does not make sense.
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F0/F versus Concentration of Quencher is a straight line, but I am unable to calculate the binding constant and number of binding sites.
Moreover, what will be the unit of the binding constant? Is it necessary to take the molar concentration of quencher?
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But you should specify the M-Ln complex( like Ru (III) bpy3 / Rh complex ) as well as quencher ( like Fe ( H2O)6 or Iodide ion , I - ) complying Stern - Volmer kinetics .The standard fluremetric data is to be analysed for correlation coefficiant ( r ) lies
in between or less than 1. This data analysis signifies a linear with relevant value of r proves the co-ordination number of metal M like Ru , Rh complexes are hexa-co-ordinated ( n=6) .
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Hello! I have a problem with a reformer kinetic implemented in Aspen Plus. I have a PFR reactor that need to be closed with a recycle. In this recycle there is a very small amount of H2 that invalidate the kinetic and gives me error, this is because in the reaction rate expression, some terms are divided for the partial pressure of H2, and therefor being so small, is like dive everything for zero and that is causing problem in the converge.
Is anyone of you familiar with such problem? There is a way to "eliminate" a component from a stream is present below a certain amount?
Thank you
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Thank you very much for your answer. I am still not practical with Aspen Plus since I focused for a lot of time on Aspen Hysys, I will try to insert the design specification you suggest. I am working at 15bar and 950°C, the molar fraction of hydrogen that i would eliminate is 10^-7.
I will reach you out is any help is needed.
Thank you and wish you the best
Asya
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I guess my question is quite simple: you know how for compressible CFD codes we have the Sod Shock tube problem that we can use as a benchmark. What if I now want to expand my code and add chemical reactions to it, what would be a good/similar test problem that I could use to validate how well my code runs?
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According to the link provided above, one may be tempted to suggest a simple combustion test case involving hydrogen oxidation to validate the "in-house" developed chemical kinetics CFD code. Thanks.
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Dear all,
I have planned to do kinetic studies of Dry (CO2) Reforming of Methane experimentally and theoretically for my developed Ni/CeX-Zr1-XO2. I went through some published papers, and they have shown the final kinetics equation based on different kinetic models, which is very difficult for me to understand and perform for my experiment. May I get help from any one of you in this regard or anybody willing to research collaboration with me in these regard?
Thank you in advance for your kind consideration and any valuable supports!
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Okay, thank you Sudesh Kumar !
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Hello, I'm studying metal-catalyzed reactions between oleic acid + oleylamine (amidation) and oleic acid + oleyl alcohol (esterification). I have a general sense that, all conditions being equal, amidation should be faster, perhaps due to the basicity of the amine, but that seems sort of vague and I'm trying to get a full understanding of what I should expect. Any help would be much appreciated. Thanks!
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As reported by Nayim Sepay , these two reactions are pH-depended. Besides, the esterification of phenol is lower than that of alcohol because of the lower nucleophilicity of the hydroxyl group that results from the participation of oxygen lone pair with the aromatic resonance.
Regards,
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motivation components intrinsic motivation, self-efficiency, self-determination, career motivation, and grade motivation in learning chemical kinetics and equilibrium
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Regardless of the subject, questionnaires can be developed by the researcher with what he/she considers important or can come from other researchers (I.e., benchmarks).In general, the first contact with the social click you research must be suave, and empathic so that you get to know about them. Stress and distrust can bother students, for instance.Info about the Likert scale can be found here:
You can also use Excel (please, refer to the enclosed file), Matlab, Origin, Scilab, R and online sites to process data related to questionnaires.
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Hello,
I would like to validate my regression algorithm which calculates activation energy and pre-exponential factor from the TGA curve. It uses integral method (the exponential integral for resolving the right side of the equation):
d_alfa/alfa = -A/beta*exp(-E/R*T)dT
where alfa is the extent of mass loss, beta - heating rate, A - pre-exponential factor, E - activation energy.
I compared my results with literature TG curves but, the results differ slightly. I'm wondering if the error is caused by my calculation algorithm or uncertainty of A and E estimation is so high.
Could anyone provide a simple TG curve (one component, first-order order kinetics) and corresponding A, E, and beta - I believe that the data calculated would be the best because I should receive exactly the same A,E result during regression using my algorithm.
Best regards,
Marcin Stec
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Set aside your algorithms and calculations for a few minutes and test the following nonlinear regression curves.
You can also estimate the parameters well.
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Anyone knowing metamorphic geology would know the sequence of mudrock to gneiss transformation and its intermediate steps, including mica formation and growth (slate, phyllite, schist) and breakdown (gneiss) as metamorphic change intensifies. One may also refer to any standard petrogenetic grid to locate P-T curve for that transformation, since composition of gneiss lighter bands (plagioclase,...) and darker bands (pyroxene, amphibole...) are also commonly known. My questions are-
  • Mica being phyllosilicates with layered structure, gain what kind of free-energy lowering advantage by growing normal to direction of maximum compression instead of being growing, say, in scattered or parallel to maximum compression direction? what are the chemical factors that affect the layer spacing?
  • Similar question for generation of lamellar lighter and darker bands in Gneiss by decomposition of mica into feldspar and mafics (why layer instead of scattered blobs?). Why the free energy (magnitude and hence stability) of phyllosilicates drop at higher P/T and what is the molecular-level mechanism of this exsolution? how this transformation is different from and similar to eutectoid phase transition seen in metals? What are the factors that affect spacing of the layers (quantitatively?)
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To comment on Brian P. J. Stevens 's observation it would appear that quartz-feldspar bands have similar density versus biotite which is much lighter and "floated" on top of the other layer.
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The following data are obtained in an enzyme catalyzed reaction: [S]x10^4(moldm^-3): 2.5, 5.0, 10.0, 15.0.
Then rox10^6(moldm^-3min^-1) : 2.2, 3.8, 5.9, 7.1.
Assuming Michaelis-Menten Kinetics, calculate:
1. rmax
2. Km
3. K2
Using the Lineweaver- Burk and Eadie method.
Given [E]o = 4.0x10^-6 mol/dm^3
1. rmax- maximum rate
2. Km- Michaelis Menten constant
3. [S]- concentration of substrate
4. ro- initial rate
Check the image for clarity.
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Regardless of whether we use nonlinear regression or one of the many graphical methods, e.g. L-B, E-H or Merino, nothing will change because the number of points is too small to determine reliables values of two parameters. Additional kinetic tests should be performed for rate limiting substrate concentrations below 2.5 and above 15.
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I am looking to find a material (any type) that can offer me CO formation energy (> 2.0 eV) and NO formation energy ( < 0.5 eV) simultaneously. Secondly, how to confirm these formation energies experimentally? Your expert opinion in surface reaction, catalysis would be appreciated. Thanks
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Thank you Professor Frank T. Edelmann for the great insight. sure, I'll go through the mention linked. well, from your expertise, will you please suggest some potential materials which can show desired chemistry. Thanks
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In what case would a reaction rate always show direct relation with activation energy or would it always be an inverse relation? Is it a indirect relation, inverse relation or both case can hold? (Please provide supporting resource, thank you).
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Toyese Oyegoke when we are talking about your question and particularly the catalyst which always lowers the energy of the transition state for the reaction - in this case any reaction you can assume.The difference between the transition state energy and the other part that is the reactant energy is the main ACTIVATION ENERGY and this is very important to understand, Lowering of this energy which means lowering of transition state energy also ensures and lowers the activation energy for sure
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Trying to elucidate a reaction pathway, I calculated the energies for different transition states possible for that reaction (computational chem. DFT). I found activation free energies ranging from 29 to 39 kcal/mol, and wanted to understand if all those transition states are possible in the reaction conditions that were used in previous papers. That is, given that this reaction is known to occur at around 355 K, is it possible to overcome those free energy barriers of 29 to 39 kcal/mol?
I know I can calculate the rate constant for a given temperature using the Eyring equation but I'm not sure how to relate the rate constant to the reaction "feasibility".
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The "feasibility" of one reaction depends on thermodynamic factors and kinetic factors. When thermodynamics are feasible, then kinetic factors become the main impact we consider.
When we consider the Eyring Equation,
κ = K ( kT / h )exp (–Δ G ‡ / kT)
the Eyring Equation, developed by Henry Eyring in 1935, is based on transition state theory and is used to describe the relationship between reaction rate and temperature. It is similar to the Arrhenius Equation, which also describes the temperature dependence of reaction rates.
Two aspects should be calculated: about enthalpy and entropy.
ΔGº = ΔHº – TΔSº
Most of the time, someone consider activation enthalpy factors to estimate the reaction "feasibility" temperature. However, more accurately, the influence of activation entropy should be consideredespecially when the activation entropy is relatively large. For example, some enzyme similar-catalyzed reactions, they can occur at low temperatures even the activation enthalpy were large.
Another important thing that needs to be considered is that, in addition to the common calculation errors in DFT calculations, it often does not represent the true situation in the reaction, such as the solvation effect. Given a large or small activation energy in the DFT calculation, it does not mean that the reaction will never happen or happen, but may be caused by some factors in the calculation.
From the published literature, by comparing the calculated results with the experimental results, the results of 29 to 39 kcal/mol you gave is possible.
Pls see references of
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I wonder if the activation energy calculated based on the Arrhenius plot for a multi-step reaction is a sum of activation energies of elementary reactions or is a difference between energy of reactants and energy of the transition state with the highest energy (associated with the rate-limiting step). Maybe, it is something else?
What if the reaction rate goes down, while the calculated activation energy from Arrhenius plot decreases?
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Activation energy makes sense here for each stage separately. Exponential functions with different bases and/or exponents cannot be added together.
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Dear colleagues,
I have a reaction involving calcium phosphate at pH 6.80 in a complex system that dissociated at low temperatures (I use ionic calcium concentration), which overall is in a metastable state (not in equilibria). In details, I have calculated the order or reaction (first-order) and all the K (rate constant) using ionic calcium concentration as my C values, at different temperatures from 4 to 35C. It is known that calcium phosphate has inverse solubility and thus the rate constants are higher when temperature decreases. Therefore, is it possible to have negative activation energy (Ea) for such reaction? I read that is possible for reactions involving halogens and ozone.
Thanks
Regards,
Giovanni
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Giovanni Barone, Activation energy only makes sense for elementary reactions/processes. The value you determined is not the activation energy.
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I want to purify my insoluble organic compound from sodium chloride through washing.
I have done my first trial with distilled water having tds approx 44 p.p.m and the second with fresh ground water having tds approx 500 p.p.m.
The results differs in both trials.
So how t.d.s and hard minerals affects the solubility of sodium chloride in water?
how can i calculate the ratio of solubility based on water quality (t.d.s).
Suggestions are highly appreciated.
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Each water has a capacity to dissolve any solute. After reaching such level, the water is saturated. Thus, it is not surprizing to see high TDS water has lower capacity to dissolve NaCl, compared low TDS one
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Hello everyone,
I have been working on developing a reduced kinetic mechanism for diesel-biodiesel-gasoline mixtures. I have reduced the detailed mechanisms of each individual fuel and combined them to form the final mechanism via Chemkin software.
However, throughout the combining procedure, the Chemkin software does not offer any options to specify a quota for each individual fuel before mixing, so, please kindly guide me on how can I define a specific fraction of each fuel in the final mechanism?
Thanks
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If one go literally to what you wrote, one can think that you mean fuel blending. But, as one know, the rate at which such mixtures are formed does not affect their properties. So you probably mean something else, e.g. the mechanism of the combustion process of fuel mixtures in the engine. You should be clear about this. As for the composition, it is best to use mass fractions here.
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How to calculate Kinetic Parameters from (TGA,DSC,DTA,DTG) curve using Coats-Redfern?
I hope it will be a practical example with detailed steps, whether in Excel or Origin or any other program (entropy S, enthalpy H, G, A, K)
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A lot of information can be useful.
Best of luck
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Hi Everyone,
I am trying to do analysis of solid rocket motor with non equilibrium turbulent combustion based on Eddy-Dissipation concept. Before doing analysis, I need to have chemical reactions and chemical kinetics such as reaction rate. How can I get them on chemkin? My solid propellant consists of mainly ''hydroxy-terminated polybutadiene, ammonium perchlorate, and aluminum''. You can find list of chemical reactions in the picture that I have to find on chemkin.
Thanks
regards
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Dear Oykum Unal I found your technical question really interesting, although I'm not a proven expert in this field. Even though this does perhaps nor answer you question directly, you might find some very useful information in the following PhD thesis entitled
DEVELOPMENT OF AMMONIUM PERCHLORATE BASED SOLID PROPELLANT
The thesis can be freely downloaded as pdf file from the internet. As in your case, the studied propellant consisted of a mixture of ammonium perchlorate as oxidizer, aluminum (Al) as fuel and hydroxy-terminated polybutadiene (HTPB) as binder.
Good luck with your research! 👍
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It makes the plastic undesirable but is listed in procedure.
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Amylopectin restricts restricts starch from becoming plastic-like therefore, HCl serves to change its properties.
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Influence of ligand on an heterogeneous catalyst surface reactivity
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Thank you for sharing idea Madhukar Baburao Deshmukh
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I need thermophysical and electrical oil properties to investigation of DC discharge in oil.
Are multicomponent mixture models effective and precise in such calculations? If yes, what MC-modells can You suggest?
Can somebody advice something?
Thank you a lot in advance!
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I suppose you are talking about normal octadecane (n-C18H38).
You may try several engineering models for a reasonable temperature range up to about 600 K to 700 K. Although there are no extensive data measurements for this fluid. The one-parameter friction theory model: https://doi.org/10.1016/S0378-3812(00)00474-X, combined with the Peng and Robinson EoS can give you some reasonable pvT, viscosity, and phase behavior estimations. This approach can also be extended to thermal conductivity.
But for most of the temperature range you are looking at, the octadecane will certainly be degraded. I even doubt you will have any CH4 left at all, as it starts decomposing at about 1000 K.  
So, you need to first figure out what compounds you will have left.
But, at such temperatures, you are likely only to have some light gases and C. For the fluid phase, a simple model that may be useful to consider would be the one by Chung et al.:
I would start here.
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While surface roughness is an obvious factor, this is not what is exactly asked. Rather, periodic variation of exchange current density (of an electrode) with solution chemistry (of electrolyte) and crystal structure (of the metallic electrode) is asked, if any of these exist.
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I believe the exchange current density is at "zero" overpotential. Tafel equation relates current density to some over potential but it does not offer any insights about exchange current density when overpotential is zero.
Yurii V Geletii out of curiosity, would chrono-amperometry be useful here? The idea there is to provide a periodic modulation of the over-potential and monitor the response current decay while the overpotential is zero?
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I am using finite difference method to discretize the parabolic equation (explicit method), but confused about the chemical reaction term. Solving the generic equation for i specie involves a couple of species in the kinetic reaction equation since it is reversible ( Ex: A+B <-->C ). What is the best way to conquer the complexity in this manner? should I go with separation method and solve diffusion and reaction term separately. I am not quit sure if it is applicable. Thanks in advance.
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Please Dear Matt Mj
The books below are good for your question.
[1] BARD A.J., L.R. FAULKNER,(1983) électrochimie; principes, méthodes et applications, (chap. IIV, V) MASSON,.
[2] Gallus Z, Fundamentals of Electrochemical Analysis, (1994) Second (revised) Edition, Ellis Harwood, New York, Chap (I-VI).
[3]Girault Hubert H, (2007) Electrochimie physique et Analytique, 2ème edition, presses polytechniques et universitaires romandes, chapVIII,pp (391 -395).
Kafia OULMI
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Hello,
I am working on heavy metals removal using adsorption technique and i want to know if physical adsorption or chemical adsorption occurred. From literature, I can determine the type of adsorption from four parameters ΔH°, activation energy Ea, the mean free energy E=√(1/2β) and effect of temperature. Until now, I worked on two adsorbents but I got the following results:
For the first adsorbent (Let’s refer to it by “X”):
(1)   The obtained ΔH° value was -68 and -43 kJ/mol for Cu and Cd respectively but generally, if the values of ΔH° are 0∼−20 kJ/mol so physical adsorption occurred and if ΔH° values −80∼−400 kJ/mol so chemical adsorption occurred. How to illustrate that? Physical or chemical adsorption?    
(2)   The obtained Ea value was 112 and 159 kJ/mol for Cu and Cd respectively. The activation energy of adsorption Ea for physical adsorption is 5∼40  kJ/mol, while the activation energy of adsorption Ea for chemical adsorption is 40∼800 kJ/mol. So it is supposed that “chemical adsorption occurred”.
(3)   The obtained mean free energy E from the relation E=√(1/2β) from  Dubinin–Radushkevich (D–R) isotherm was less than 8 kJ/ mol. If the magnitude of E is between 8 and 16 kJ/ mol, it is indicated that the adsorption process is chemical adsorption, while for value of E < 8 kJ/ mol; the adsorption process is physical in nature. So according to this point it is supposed that “physical adsorption occurred for both of Cu and Cd”.
(4)   The adsorption decreased upon rising temperature for Cu and Cd (This behavior indicates that “physical adsorption occurred”).   
Now, I cannot determine the nature of this reaction if it is chemical or physical adsorption! From these results, can I say that both of physical and chemical adsorption occurred?!
For the second adsorbent (Let’s refer to it by “Y”):
(1)   The obtained ΔH° KJ/mol value was -52 kJ/ mol for Cu and -108 for Cd but generally, if the values of ΔH° are 0∼−20 KJ/mol so physical adsorption occurred and if ΔH° values −80∼−400 KJ/mol so chemical adsorption occurred. So according to this point it is supposed that “chemical adsorption occurred for Cd” but what about Cu in this case? 
(2)   The obtained Ea value was 28 kJ/ mol for Cu and -58 kJ/ mol for Cd. The activation energy of adsorption Ea for physical adsorption is 5∼40  KJ/mol, while the activation energy of adsorption Ea for chemical adsorption is 40∼800 KJ/mol. So it is supposed that “physical adsorption occurred for Cu” but what about cadmium in this case?
(3)   The obtained mean free energy E from the relation E=√(1/2β) from  Dubinin–Radushkevich (D–R) isotherm for Cu and Cd was < 8 kJ/ mol. So according to this point it is supposed that “physical adsorption occurred”.
(4)   Upon rising the temperature the adsorption increased to a certain temperature then it decreased (This behavior indicates that chemical adsorption occurred) where with increase in temperature, chemisorption first increases as sufficient energy is being provided for the molecules to reach the activation energy. But after certain degree it decreases, as the further high temperature helps in breaking of the bond between the adsorbate and the adsorbed molecules. So according to this point it is supposed that for Cu and Cd “chemical adsorption occurred”.
In this case also, I cannot determine the nature of this reaction if it is chemical or physical adsorption! From these results, can I say that both of physical and chemical adsorption occurred?!
Kindly, help me to write a plausible interpretation for these confusing results. I really appreciate your help and your time to read my questions.
*   The attached file is a reference for points (1) and (2) so you can review it.
Thank you.
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We are in need of some software with which we can use templates of chemical isotherms like Langmuir, Freudlich, BET and others, and also chemical kinetics to get k value, linear graphs, non linear graphs, etc.
Literature is available and I am searching for a software or preprogrammed software (Exel/origin/others) along with templates with which I can draw graphs for the above and go ahead with interpretation of data.
I have huge data base collected from lab work and want to to process the data for these parameters with accuracy and confidence. Topics covered ranged from chemical adsorption, electrochemical methods of metal removal, COD removal, microbial and biotechnological methods for the same pollutants (almost).
Experts, please guide me in this regard, if any free software is available or even for purchase along with due instructions, etc.
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Here is link visit this channel
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I am wondering what will happen to the molecule if it's HOMO-LUMO gap will approach to zero.
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The energy gap between HOMO and LUMO also helps to describe the chemical behavior and electrical properties of molecules, with lower energies indicating higher reactivity and lower stability
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Could the presence of ligand on a catalyst surface reduced the reactivity of its surface? If yes/no, please explain why?
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this depends on which type of ligand used
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we are working on metal sorption by  biomass and  our data is obeying both Langmuir and Freundlich isotherm in terms of R2 value between 0.8-0.9, then which adsorption constt is (Q0 or Kf )will better describe sorption capacity of biomass and what type of interaction it will follow
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How to apply Langmuir adsorption isotherm. A complete guidance ..
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I want to know how to do interpretation from the graphs, please give reference if any & what is difference between them ? 
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Pseudo first order kinetic model.a complete step by step process..
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1. Can anyone provide me the basic step by step protocol of Langmuir and Freundlich isotherm parameters for adsorption of pharmaceutically active compound (carbamazepine) from aquatic bodies using plant extract capped magnetic nanoparticle
2. how to calculate the Sorption and desorption experiment setup?
3. how to calculate the absorption kinectics? 
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Freundlich adsorption isotherm a complete guidance
… Read more
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I am trying to reduce a detailed mechanism, through various reducing methods such as DRG, DRGEP, Full species sensitivity analysis etc. What will be the final developed mechanism called? I mean whether it will be called skeletal mechanism or reduced mechanism? What is the difference between skeletal mechanism and reduced mechanism?
I am a mechanical engineer and have very little knowledge of chemical kinetics. Please suggest me some books or literature that can be helpful to understand the basics of chemical kinetics.
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The skeletal mechanism is a detailed mechanism considering both sensitivity and flux analyses where as the reduced mechanism to consistently over predict the temperature .
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I have been using chemical kinetics equations (1st order, 2nd, order, etc) for modeling of adsorption /desorption of drugs on molecular sieves. Is this a correct or I need specific equations? I need good references . Can someone help me?
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Hi,
Like other molecules, the kinetics of drugs adsorption can be presented using various existing models. These are some of the articles related to adsorption of emerging contaminants conducted by my team for your future references, if applicable.
ATENOLOL SEQUESTRATION USING ACTIVATED CARBON DERIVED FROM GASIFIED GLYRICIDIA SEPIUM, October 2020, Arabian Journal of Chemistry 13:7544–7557
DOI: 10.1016/j.arabjc.2020.08.029
Amino-functionalised silica-grafted molecularly imprinted polymers for chloramphenicol adsorption, May 2020, Journal of Environmental Chemical Engineering 8(5):103981
DOI: 10.1016/j.jece.2020.103981
Ordered mesoporous carbons originated from non-edible polyethylene glycol 400 (PEG-400) for chloramphenicol antibiotic recovery from liquid phase, January 2015, Chemical Engineering Journal 260:730-739
DOI: 10.1016/j.cej.2014.09.010
Riboflavin adsorption onto multi-modal mesoporous carbon synthesized from polyethylene glycol 400, January 2013, Chemical Engineering Journal s 215–216:297–305,
DOI: 10.1016/j.cej.2012.10.031
Regards,
Azam
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Both these phenomena are termed catalysis, but clear and complete discussion and specification of their similar and distinguishing features would be useful.
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Heterogeneous catalysis the phase of catalysts differs from that of the reactants or products. On the other hand homogeneous catalysis the catalyst is soluble forms a homogeneous mixture with the reactants . The common feature in both types of reactions reaction occurs at the surface .The rate depends upon the amount of the reactants and nature of the substrate. Sterically crowded substrates may undergo the reactions less readily in both the cases.
and products and ... the surface.
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Is the topic 'prediction of hydrate conditions in gas pipeline' a chemical kinetics research work
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Good day everyone. i am required to develop a model for gas hydrate calculation can anyone assist me on how to do it
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I have seen people using 1.39 µm, 2,5 µm respectively. Currently, I am working with 1,392 µm to measure H2O. Also, one can choose the appropriate wavelength from the 'spectraplot' as well. Can anyone really suggest or have worked with a shock tube using TDLAS to study Chemical Kinetics?
Your valuable feedback in this regard would be really helpful. Looking forward to a response.
Thank you.
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Dear Sumit.
I would recommend to get in touch with the Hanson lab in Stanford. They have done lots of laser spectrosopy in shock tubes, in paticular detection of H2O. On their website (hanson.stanford.edu) you will find the PhD thesis of Hejie Li from 2007 where you can find details on the 1392/1398 nm absorption lines. In a later paper (J. Phys. Chem A, 2010, 114, 18: 5718-27) they measured time histories of H2O in a shock tube using 2550.96 nm (this might tell you already something).
I hope that helps,
Wolfgang
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If I have a method for the measurement of kinetics parameters, how I can determine the different concentrations of substrate that I need use for obtain several initial velocities and generate the Lineweaver-Burk plot? and what kind of software is recomendded for the calculations?
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Engelbert Buxbaum, Well, we will discuss it one each other.
There is "linear regression". There are minimization methods with the objective function in the form of one of fit measures, commonly called "nonlinear regression". I still do not know what is "linearizing regresion". By changing the coordinate system, a straight line can be obtained from the data in the form of a curve, but it is not a linear transformation or a linearization. Likewise, they are not a linear transformation of L-B, Hanes-Woolf or Eadie-Hofstee transforms, or taking log. So you did not convince me of the sense of using such a term.
You have your favorite method and I have mine. You had interesting experiences with NM, me with ML. Among other, I used it to solve two-point boundary value problems for ODE, to minimize G (equilibrium composition of reaction mixtures), or to determine the parameters of kinetic equations. As I wrote earlier, ML can be used for any function, whether in the form of a formula or an algorithm. I also used NM (2nd step) in conjunction with the Monte Carlo method (1st step) and the FPD method (3rd step) called MINUITL from the CERN numerical program library.
You ask for chi2. There used to be an ML routine in the CERN library with a built-in SRE (sum of relative errors) instead of SSD. But with chi2 I did not see. Regards,
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i have done mtt assay many times..but unfortunately i couldnt acquire proper absorbency for my conditions even for my controls...the absorbency of my control isnt higher than 0.5---i dont know what should i do??
i have seed 15000 and also 25000 cells in each ninety six well plate but i couldnt get good result?
Does anyone have any idea about my problem?
many thanks
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Navid Jamali Hi, I am facing a similar problem as you. I am using NHDF cells for MTT assay. During my cell density optimization, I got an absorbance value of 0.6 even with 40,000 cells/well (100ul). They are untreated and I allowed them to grow in the 96-well plate for 24 hours. Do you mind sharing how did you troubleshoot this problem?
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I want to get the maximum concentration for carbon dioxide in an 0.5 M potassium bicarbonate solution
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The article Radomir I Slavchov shared are good
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Hello everyone,
Has anyone please manage to write a code for the methane reduced mechanism mentioned in paczko's paper named "Reduced Reaction Mechanism for Meathne, Methanol and Propane Flames"? Because i don't know how to initialize the domain with zero concentrations of species H, H2O, CO, CO2, H2, M while they are needed in calcualting intermediate species.
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Yes, they are correct according to the published paper. And i thought the same as you told me. Thank you so much for your interest and effort.
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I am doing H-abstraction reaction by OH radicals. I found one TS, Which is barrierless. Is it possible. What  is reason behind it ?
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I would like to thank to Prof. Karaman for his explanation and the references.
We experienced several barierless TS in calculations of organic radicals binding weakly Br. radicals. In some cases this was apparently not due to thermochemical corrections (as reported in some references known to us) but due to an entropy penalty for some of the intermediates. We would like to understand the phenomenon (if not resulting from a method artifact) better, hence I am grateful for any hint.
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I am doing a kinetic study on an enzymatic reaction which does not follow Michelis-Menten equations.
I am using a model to fit the experimental data, and it can fit the data for each given substrate concentration (mixed with different enzyme concentrations) very well, BUT the rate constant changes by changing the substrate concentration. In other words, the rate constant seem independent of the enzyme concentration, but somehow dependent on the substrate concentration. It should also be mentioned that in all conditions, the substrate is excessive.
I am wondering if this phenomenon is physically possible or something is wrong with the model.
Thanks.
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  • There could be an allosteric effect of the substrate by binding to a second site.
  • The substrate could be contaminated with an alternate substrate or an inhibitor.
  • The substrate may be having a non-specific effect on the enzyme, such as acting as a denaturant, or causing a shift in pH, or increasing the ionic strength.
  • If the reaction is metal ion-dependent and the substrate binds the metal, the concentration of free metal ions may be decreasing as the substrate concentration increases.
  • The substrate could interfere with the method of product detection.
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I am looking for method.
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It will depend on the shape of your DTG curves. The peaks (and shoulders) will show you the temperature range for the main pyrolysis reactions. Most biomass materials have 300 - 600 degC as the main pyrolysis temperature range.
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It would be helpful if you could mention a reference that discusses the effect of different chemical kinetic mechanism to the emission predictions.
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Through the assumed reactions pathways and their final products and kinetics rates parameters. For global two step reactions, it the reaction rate of the CO oxidation will the rate-limiting or controlling rate for the CO2 emission. Same thing if you have other small radicals in your mechanism. Conduct a sensitivity study to determine which reaction(s) are the important ones for the emission species being investigated.
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Hello,
I'm looking for a good reduced or detailed chemical mechanism to simulate methane nitrous oxide premixed flames.
SanDiego mechanism (with nitrogen chemistry "add-on) and GriMech3 are both disappointing when it comes to predicting laminar flame speed.
The following article worked on an other mechanism named PPD, is this the most accurate mechanism nowadays ? Thanks
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Dear Etienne Testard,
in 2019 Krishna Prasad Shrestha et al. presented a paper on this topic ( ) and further also on Methanol and Ethanol combustion. Maybe his reaction mechanism can help you to get better results.For my calclations with Methane and hydrogen mixtures the mechanism worked quite well
Combustion Science and Technology
DOI: 10.1080/00102202.2019.1606804
and
Fuel 261
DOI: 10.1016/j.fuel.2019.116349
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I am interested in knowing the equations for obtaining these properties and subsequently inserting them in a model.
Suggestions on texts, articles and web materials will be appreciated.
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I guess you mean effective values. Then not only porosity, but a tortuosity factor is needed. It is better, however, to measure yourself.
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Hello
I want to calculate rate constants for CuO or Cu2O crystal growth formation. Please suggest an experimental or simulation technique to do that
Thank you
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Tania Avianda Gusman When we observe the transformation (crystal growth) of our molecules in a polarized optical microscope, we capture every moment at transformation. For example, every 1 sec or 30 sec etc (the choice is ours depending on the speed of crystal growth), we capture one image. With collections of images at fixed duration, we now have a bunch information about (1) average crystals size (in micrometer usually) which can be calculated using the software given by the microscope and (2) time (in seconds or minutes). The constant rate of growth can be calculated by plotting at least seven data points (the more the merrier) of (1) divided by (2). Please also note that the magnification settings and calibration shall be adjusted well for accurate calculation. Hope this helps.
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I am working in the computational field of gas phase kinetics. Right now I am doing some unimolecular decomposition reactions. I want to calculate the rate constants of these reactions using RRKM Mesmer.
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Please send me your mail or you whatsapp number . I will explain you as completely.
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I am trying to find the best model to my data. The velocity (V) vs substrate [s] curve looks hyperbolic under normal conditions. When I introduce an inhibitor of interest at concentration of, say, 1 mM, the curve is low and flat. However, when the concentration of my inhibitor is at 0.5 mM, the curve is lower than the normal, but has a sigmoidal shape. This also occurs when the inhibitor under 1 mM is mixed in with one of its products of hydrolysis. Since the MM fit is not appropriate for all my curves I am looking at others, including the Hills equation because I believe the difference in shape has something to do with allosteric sites on my enzyme. I have a few questions:
1) I have been using the least squares method and Solver on Excel, with  'Vmax', 'Km' and 'n' as variable cells. These values are different for every curve, one results in n<1 and the rest n>1. Am I solving correctly?
2) Am I using the right model and how do I know?
3) It appears that Vmax decreases and Km increases with increasing concentration of inhibitor. I can't figure out what inhibition this is.
Many thanks
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Hi Elena,
Thank you very much for your detailed answer.
All the best for your future research.
Melanie
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I'm trying to simulate pulsejet engine combustion using a matlab code, but i'm stuck at the combustion phase.
1) I should use "G. PACZKO, P.M. LEFDAL AND N. PETERS" mechanism mentioned in (REDUCED REACTION SCHEMES FOR METHANE, METHANOL AND PROPANE FLAMES), the problem here is i don't know how to implement a reduced chemical kinetic mechanism using the paper's definitions (global reaction rate and how to relate it to the molar concentrations of the species variation with time) ?
2) How do i implement that chemical mechanism in NS equations ? when to call it, what does it need as inputs, what will it give me as outputs, .. etc.
Any help would be so appreciated.
Thanks all
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Hello, i do not know how a quasi 1d analysis of pulse jet should look like. Since there are pulses of combustion you would need a proper time resolved solver. Due to the nature of the different phases you would need to resolve chemistry in transients, though you need a fast solver which could adapt its time step size. Even if you are able to write (or use an existing solver in Matlab) for ODEs it will be very slow. Depending on which model (reaction mechanism) you are going to use to model the fuels it will very likely become very very slow. So slow that you can not do any model development with this.
I admit they i never modelled a pulse jet myself, but my knowledge is based on modelling flames, engines and furnaces in different models from 0D to 3D. I also worked with difference solvers a lot. If you want to solve chemistry on the fly, is strongly suggest you use an already developed chemistry solver. Writing your own will need all your worktime and you will have no time working on the actual model.
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Or C 's reaction with B will be limited or lesser ?
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Thanks all
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Guys,
I've seen the Modified Arrhenius equation in several forms. For instance, three kinds are attached.
Please consider the first attachment. There is an activation energy (Er). In some cases, authors do not use this form and they use the form just like two other form (see ar-2 and ar-3). They use "thetha" or "Tar". Now, I need to calculate Er from thetha/Tar. I think I have to multiply thetha or Tar by R. Am I right? R is universal gas constant and here its unit here is J/kgmol-K. I guess it should be 8314. Am I right?
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Roh,
I'm happy you find your answer. But note that everybody is free to answer as they desire. It is up to you to decide which one work for you. Their answers are also valuable but might not point out what you meant. Then simply ignore them. They may be of interest to other people who have a similar question in the future.
Good luck.
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Question: Calculate the equilibrium value of vacancies concentration for copper per atom of the order of 10^4 at 1000K the energy for vacancy formation is 0.9eV/atom.
Answer:N=N_0+exp(−Q/RT)is something that I know.However all that I could arrive is to calculate −Q/RT which calculates to give me 82.1.I have taken R to be equal to 0.0821 units and have taken T=1000K. Now I cannot proceed any further.I am not even sure what I am to calculate.
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Sorry, in my answer I vorgot the C0 . The correct formula is:
C=C0 exp-(Q/kT).
C0 is not temperature dependent and is defined by the local change of entropy if 1 vacancy is formed. C0 should be taken from experimental literature, since it is not easy to calculate theoretically.
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I calculated activation energies for intermediate stage of sintering for alumina+tetragonal zirconia composite and alumina+cubic zirconia composite via non-isothermal CHR method in microwave hybrid sintering, and compared them. The particle sizes of both as-received zirconia were same. A+tZ shows slightly higher activation energy as compared to A+cZ, but the densification of A+tZ is also higher. Can someone please guide? Because if densification is higher, then the activation energy for sintering should be lower, but that's not the case here. Is some unusual factor of sintering kinetics involved here?
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Activation energy for a sintering is a system property, namely: the energy barrier which system must overcome to start sintering process. In the discussed case, obviously, the estimated activation energy is a combination of surface/grain boundaries/volume diffusion activation energies of the mentioned materials system.
On the other hand, densification is a sintering result. So, is sintering parameters permitted to overcome the energetic barrier, a sintering process was initiated and then resulted in a certain final density.
Taken into account the mentioned above, I do not see any contradiction between high activation energy and high sintered density, if sintering process was adjusted and optimized specially to the mentioned materials system.
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Dear experts,
I am dealing with the synthesis and characterization of PIR foams. In particular, I am monitoring the kinetics of these foams by FTIR (please find the spectra attached below). As well-known from the literature, the asymmetric CH stretching band at 2972 cm-1 (which remains constant during the reaction) is typically used as internal reference band to correct the density changes during the foaming process. In the same way, my question is if you know from the literature some reference band that may be used for PIR to the same purpose.
Please note that for PU a polyether polyol is used, while for PIR is used a polyester polyol.
Thanks in advance.
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You can use any band based on the chemical groups that do not show changes during any chemical reactions or physical reactions. However, majority of the IR bands are the contributions from multiple groups and, thus, tend to change the intensity by either chemical reactions or physical structural changes. Aliphatic CH stretching bands, in the region of 3000-2800 cm-1, are usually very stable as the potential energy distribution of these bands are nearly 99% pure. In the case of PU, you have relatively well isolated 2972 cm-1 band. However, PIR lacks this band. Yet, there are multiple bands between 2950 and 2850 cm-1 that appear to be relatively stable. Ideally, you should curve resolve these heavily overlapped bands (there are at least three bands, maybe 4) to be more accurate, but by measuring the height (absorbance), you can obtain quasi-quantitative comparison. Use the intensity of one of the band (the one near 2850 cm-1 might be good) and divide the absorbance of the band you want to compare to normalize the intensity then compare the normalized intensity of two different conditions, such as different reaction times.