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# Reaction Kinetics - Science topic

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For the elementary reaction: HO2 + O <=> OH + O2, If G (which can be regarded as an oxygen isotope) is used to replace one of the O in HO2, make it become HOG, which of the following reaction formula is correct? Or both exist, but at different rates?
a: HOG + O <=> GH + O2; b: HOG + O <=> OH + OG;
I know some common sense (for example, the law of dehydrogenation of hydrocarbon fuel), but I am not clear about such elementary reactions.
I wish you a wonderful day.
I appreciate it if anyone can offer any help.
Yes, this is related to the bond energy. You need to dig thermochemical data and do calculations. Just a small hint
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Method for calculating reaction kinetics
The equation of Michaelis-Menten is commonly used to describe the kinetics of enzymatic reactions
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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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Hello,
This might be a very ridiculous general question but here we go:
I am trying to find kinetic parameters for the metabolism of a drug by the enzyme CYP3A4. The problem is, all literature Vmax values are specific activities either in pmol/min/mg or pmol/min/pmol CYP3A4, but I need Vmax values to be in the form: mol/h or mol/(h*L) ( for a systems biology application that uses these units in rate laws)
I am not an expert on enzyme kinetics, so I am not sure how one makes the conversion to fit the Vmax data into a this format. Do we need the enzyme concentration (in g/L or in M), as well as the incubation volume?
Some insight would be highly appreciated.
Vmax depends upon and is, ideally, directly proportional to the concentration of the enzyme. Specific activity divides Vmax by the amount of protein present (typically in mg, as in µmol/min/mg). Specific activity can be used to describe the level of activity of any enzyme-containing preparation, without requiring that the enzyme be purified.
kcat divides Vmax (in concentration units) by the enzyme concentration to get s-1. Purified enzyme is normally used for measuring this parameter.
You can express the enzyme activity in whatever way suits your needs, but you should be explicit about how the calculation is made, the source of the enzyme, what protein concentration was used, and the specific activity of the preparation so that others can repeat the work.
If you keep the enzyme concentration constant throughout all experiments, and its activity remains constant throughout, then, for the sake of your calculations, you can leave Vmax in the form of moles of product formed per unit of time or, dividing by the volume of the reaction, as concentration of product formed per unit of time.
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The rate of a chemical reaction is typically given by r = k[A][B] where [-] indicates concentration. However, it seems to make sense to use r = k{A}{B}, where {-} indicates activities, since the activity represents the effective concentration. I've found two papers that use this method for the hydration kinetics of carbon dioxide, with good results:
However, in the classic work on "Gas-liquid reactions", Danckwerts says the following:
"It is a mistake to suppose that, when the reactants are non-ideal solutes, thermodynamic activities should be substituted for concentrations in the rate-equation, and that the corresponding rate-constant will then be independent of composition. This formulation is misconceived in principle, and in practice the use of concentrations usually leads to somewhat better results that the use of activities"
I know the Danckwerts book is from 1970 and the papers above are from 2007 and 2010, but they knew their stuff back in the day! What has changed? Why is this formulation misconceived? And who is right?
Lastly, I know the rate equation is itself a simplification of the actual process, but if I want to get an accurate estimate, should I use concentrations or activities?
At the risk of not adding a lot to the conversation and speculating about someone's thought process, an possibly being spectacularly wrong, I will point out the final bit of the Danckwerts quote has two parts: 1) This formulation is misconceived in principle and 2) and in practice the use of concentrations usually leads to somewhat better results that the use of activities. I would suggest that this second part may have been the key take-home point at the time. Given the state of computing, data availability, analytic techniques, etc. one would be better served by using the concentration approach. For part one, I must confess I don't quite follow why the term misconceived was used - the discussion of Dr. Geletii and others seems correct to me. Perhaps though the key is in the previous sentence which states that "the corresponding rate-constant will then be independent of composition" is the problem. That is, the point of concern isn't about the activities per se, but that the rate constant is found to variable (not constant) in that situation. Looking back to the second point, is this really saying that the activities of non-ideal solutions were inadequately being modeled?
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Reaction kinetics for 1-Butene Epoxidation is very limited and difficult to find. However, the propene epoxidation reaction kinetics is available. Will the difference in constants and other parameters will be huge? Can I use this for education purpose? Is there any way we can get the kinetics of Butene Epoxidation from Propene Epoxidation kinetic parameters ?
There is the problem of steric hindrance in the substrate: 1-butène, which must be considered in the mechanism of the kinetics of epoxidation .
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we need the reaction kinetics for light naphtha isomerization when catalyst pt base on chlorinated gamma alumina is used.please guide us, in which book or article we can find it.
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Could TOF be affected by any catalyst properties or reactor conditions? Please share more light on the choice of your answer (other than Yes/No) and if possible provide supporting materials. Thank you all.
Thank you Sina Safavi
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I have obtained zpe corrected energies for reactant, TS and product states. I can plot a general scattered plot using MS Excel (but not that great). I would like to know how to plot a reaction profile as one would find in publications.
I have also attached my suggested excel worksheet below.
Thank you
D L S Dinuka
P.S. I need to compare several candidate profiles overlapped so using IRC method wasn't successful.
Chemdraw 2D, Chemdraw 3D, MATLAB and paint software are the good selections to perform the PES curve. Best regards.
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Actually, the apparent activation energy is that in the presence of the catalyst in this case. The suitable reactor design facilitates the mass transfer inside the reactor and consequently increases the catalyst efficiency instead of having dead zones in the reactor in the case of poor design. The net result is an increase the rate of the chemical reaction
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I have to calculate the order of reaction and reaction kinetics for a reaction which needs to be run in semi batch mode due to high exothermicity. How can I possible run an experiment and when the samples should be collected in order to plot C vs.t graph. The conversion is very fast so how do I know the concentration of unreacted is from the initial time t=0 or from the addition due to semibatch mode?
I suggest you adding internal standard to your reactor. That means you can calculate conversion using internal standard method. If it's possible, you can collect your reaction mixture on line (take little sample to analysis) after a cooling sampling line. Some instrument manufacturers could modify equipment to solve this problem, like adding quantitative loop to GC analysis.
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CFD modelling is a useful tool to examine the performance of electrochemical cells for specific reactions over suitable catalysts. Currently, I am working on using CFD modelling framework to describe coupled mass transport, hydrodynamics of flow, chemical (homogeneous) and electrochemical (heterogeneous) reaction kinetics in an electrochemical flow cell for a specific oxidation reaction on an electrode.
As I plan to use Ansys Fluent, could anyone share very useful training resources (books, videos etc.) that can assist me to smoothly kick-start this project?
You can try learning from here as well. It starts from basics and has used common heat transfer examples
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I would like to know which of these reactors is expected to record the highest conversion for CSTR and batch reactor when both reactors are assumed to have a similar volume, geometry, operating condition, and stirring rate (if possible do provide supporting resource/reference).
Thank you as you share your experience.
Toyese Oyegoke alrady the expert comments from Dr Prem Baboo has nailed it and wow loved his answers and the explanation as well thankyou Prem Baboo and being from the same industry it is always good to find like minded people
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I would like to get the concept of what it is all about and relevant supporting materials would be appreciated. Thanks to you all.
Dear Toyese Oyegoke,
I have attached some books about Surface Science and Catalysis. I hope they would be useful.
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Hello researchers,
I'm doing a gasification simulation, the problem I'm having is finding an equation that describes the pyrolysis reaction kinetics of the biomass I'm working on. Please give me your opinion on this matter.
Thanks
I expected relevant data to be available in the literature. However, I am thinking about the equilibrium model. The lack of equilibrium constants is not a problem when using Aspen. But treating the oxidation of carbon and carbon monoxide as reversible is unacceptable to me. It is also not understood to analyze a linearly dependent system of chemical reactions. I also have doubts about the second publication, where only the reaction rate constants are given. Were all the reactions mentioned in the publication first-order?
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I want to model biomass pyrolysis by the following reaction set:
Biomass = CO
Biomass = CO2
Biomass = H2
Biomass = H2O
Biomass = CH4
where Biomass is a non-conventional solid, in a RCSTR reactor. Can I do it and if I can how?
I need to mention that Biomass contains C,H,O according to its ultimate analysis.
I also attach the model that I've tried to setup to solve this problem. If anyone can help me, I would appreciate it.
The use of the Gibbs reactor model in Aspen Plus/HYSYS does not require much data for it to predict the product based on the thermodynamic condition of the process. You are not expected to provide a reaction set instead, you are to provide all possible compounds that is expected to participate in the process. The simulation of the model is expected to predict the distribution of the product based on thermodynamic conditions provided in the modeled process.
Check it out Pavlos Kostopoulos
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I am considering methods to analyze the reaction kinetics of conversion reactions in aqueous medium. I know pH-stat titration can monitor it. Can IES be used the same way?
Thanks for the short but encouraging answers.
I would appreciate a method suggestion such as polarization, potentistat charging, noise or fast fourier analysis for the monitoring of fast reactions. Some methods will miss what's happening on the electrode due to long measurements
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A solution having 2 compounds in it whose degradation is measured by checking absorbance. How can we measure absorbance of such a solution when lambda max is different for these 2 compounds?
You can follow the decrease in their wavelengths unless they interfere with each other.
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For example, let's say if I design a conversion reactor and give inlet temperature,pressure,composition and reaction kinetics then Hysys will show me the outlet conditions. It doesn't,however,show the process or how it got the results i.e calculations.
Dear Shaheen, based on the example that you have mentioned, HYSYS only do the calculations establish in a energy a material balance. Also, you have to write down the stoichiometry of the reaction. Then HYSYS perform the mass and energy balance in the same way that it has described in Elements of Chemical Reaction Engineering 6th Ed - H Scott Fogler or Basic Principles and Calculations in Chemical Engineering (8th Edition) for example. All calculations performed by HYSYS are of public domain and you can find also in the Perry's Chemical Engineers' Handbook, 9th Edition.
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When there is the Thiele modulus and the effectiveness factor to determine the pore resistance in catalysts, why do we need the Wagner modulus?
Wagner model is a rheological model developed for the prediction of the visco-elastic properties of polymers
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I search for a long time, only the reaction mechanism of RDX is listed on articles, however, is there a archived chemkin format file for the RDX reaction mechanism? as well as the thermo and transport data?
Any help or information will be appreciated.
Dear Li Deng, this question is addressed in the article shown below. The paper is available on RG.
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I'm stopped since I failed to calculate wave impedence.
Especially, relative permittivity and relative permeability are big obstacles for me to solve.
What I'd like you to do for me is not let me know how to calculate easily(of course, I'd thank you for it),
it would be even very thankful to you if you share me with books addressing this, with book names together.
Thank you for reading my question. I hope you help me.
Wave impedance: At a point in an electromagnetic wave, the ratio of the electric field strength to the magnetic field strength. (188) Note 1: If the electric field strength is expressed in volts per meter and the magnetic field strength is expressed in ampere-turns per meter, the wave impedance will have the units of ohms. The wave impedance, Z , of an electromagnetic wave is given by
📷
where is the magnetic permeability and is the electric permitivity. For free space, these values are 4 × 10-7 H/m (henries per meter) and (1/36) F/m (farads per meter), from which 120, i.e., 377, ohms is obtained. In dielectric materials, the wave impedance is 377/n, where n is the refractive index. Note 2: Although the ratio is called the wave impedance, it is also the impedance of the free space or the material medium.
In the following website you find and example and solution to calculate wave impedance.
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Hello All,
In order to make some calcium test devices, we will be needing to expose calcium pads (100 nm of thickness) to nitrogen atmosphere. We do not expect the exposure time to be more than a few minutes. Twenty minutes could be considered a safe upper limit.
I am wondering if anyone who has had a similar experience can tell me if this would lead to severe degradation of the calcium pads.
The oxygen content inside the glovebox is assumed to be less than 1000 ppm. I have reaction rate data for oxygen, and I can take care of that. I'm mostly concerned with reaction with nitrogen itself, for which I have not been able to find any reaction rate data.
Thanks,
Pouyan
Dear Pouyan
In my experience of testing Calcium thin films, the oxygen and water are predominant factor to react with Calcium. According to literatures, Calcium can only react with nitrogen to become calcium nitride under 200 to 450 degree C. Controlling the oxygen and water levels inside the glovebox is critical to fabricate calcium present devices. When we made devices with a calcium layer involved or pure calcium layer, the degradation can start after two hours. Therefore our devices had to be encapsulated within 1 hour. The OLED devices I can kept for 5 years were still lit up. They had hardly any black spots. The most importance is to control oxygen and water levels inside the glovebox. You mentioned that you assume the glovebox is less than 1000ppm. This figure is far far too high for any calcium layer presented devices. Our glovebox was kept both oxygen and water levels less than 0.1ppm.
Hope it helps.
Best wishes
Xuhua
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Hi every one,
I'm working on developing a reaction kinetics for a set of 100 sub reactions. most of the elementary reactions has a clear k value but some of the acidic reactions have just the PKa value. How can I involve these reactions in my overall kinetic equations?
should I find k+ and k- (forward and reverse reaction k values) for these reactions?
Thanks
You have duplicated your question. Delete this one.
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Hi every one,
I'm working on developing a reaction kinetics for a set of 100 sub reactions. most of the elementary reactions has a clear k value but some of the acidic reactions have just the PKa value. How can I involve these reactions in my overall kinetic equations?
should I find k+ and k- (forward and reverse reaction k values) for these reactions?
Thanks
Commonly, the protonation step (k-) is a diffusion controlled step. You can safely take k(-) = 1e+10 M-1s-1. Then, k can be calculated from pKa.
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I just want to perform the kinetic study of pollutant degradation by H2O2. But how can we stop the H2O2 reaction after the sample collection at different time Intervals before the test of the collected samples. Please suggest me any possible way to stop the H2O2 reaction after the samples collection.
MnO2 accelerates the decomposition of H2O2 (catalyses). Could you use this principle? For example at a certain time collect the sample and then add MnO2 to get rid of H2O2 quickly and then look for concentration of original pollutants remaining? You may get a pseudo rate constant for the pollutant decomposition using this method of collecting kinetic data
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I am trying to calculate the reaction rate constants (k) of chemicals and this is usually given in units of cm^3/mol*s or a variation thereof. However I came across a few papers that gives it in 1/Torr*s and I am not sure how to convert it to cm^3/mol*s for comparison with other reaction rates.
just from the units you gave it is not possible since there is no way to convert kg in m² without any additional assumptions.
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What are the kinetics of the reaction between aqueous solution of ferrous chloride and chlorine gas, can it be considered as a diffusion process with chemical reaction?
All elementary bimolecular reactions include diffusion of reactants to form a collision complex. The kinetics strongly depends on concentrations, pH, ionic strength, etc
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Hi,
I'm doing a group research project at university and we are struggling to find reaction/kinetic data for very-long-chain fatty acids (C-18 to C-24), and was wondering if anyone would be able to point me in the right direction?
Trawling through online articles is currently leading me round in circles and so far no book I have access to has been of use.
I am unable to carry out an experiment to obtain the data myself, hence why I have been looking elsewhere.
Thank you in advance for any help!
Hello, …… before getting the kinetic data of a reaction, think to simulate the reaction to get these data. verify your results based on the output of the reaction, eg. reaction temperature, viscosity, ….etc.
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I just need the k-constants or values that will help me model the reaction
If you are going to build kinetic models you must learn how to dig the necessary data. You are supposed to know that the Nobel Price was awarded for studying the rates of acid base reactions.
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For my adsorption system I need to calculate thermodynamic parameters. For the study I used 3 equations
1. ∆G = −RT lnb (b is the Langmuir isotherm constant)
2. ∆G = ∆H −T∆S
3. ln b=- (∆H/RT)+(∆S/R)
When I plot the graph of ln b Vs 1/T. I got a positive gradient and a negative intercept. Giving a negative ∆H, ∆G, and negative ∆S.
Is it possible to have such values and a graph and is the graph acceptable with a positive gradient?.
The following articles introduce the most correct manner for calculation of thermodynamic parameters and contain valuable explanations about this subject.
Journal of Molecular Liquids Volume 273, January 2019, Pages 425-434; Journal of Molecular Liquids Volume 280, 15 April 2019, Pages 298-300
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Hey chemistry community :)
I want to measure how fast radicals are produced by the reaction APS and TEMED. Does anyone know how one could do this? Is UV/Vis possible?
Thank you
The C-centered radical will quickly react with O2 forming peroxy-radical, which in its turn should react with ABTS. I would suggest you to purge your solution by O2.
TEMED pKa: pKa1 5.85; pKa2 8.97. pH should >9 to have deprotonated TEMED
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How can I calculate the activation energy and frequency factor of a reaction where the reaction rate increases with temperature until a specific temperature and after that the reaction rate reduces with rise in temperature?
I believe in a normal reaction case (i.e., reaction rate is proportional to temperature), the activation energy and frequency factor can be calculated from the slope and intercept value of a line plotted with time vs ln (slope of fitting equation), using Arrhenius law.
I am looking forward to your suggestions.
You can use the Arrhenius law in logarithm form to get the forward activation energy and forward rate frequency using only the ;lower temperature section of data.
Ln (k1) = Ln (A1) - E1/RT
The same equation can be used with the highest temperature section of data to get the reverse activation energy and backward frequency.
For exotherm the reverse activation energy should be higher than the forward activation energy.
Ln (k2) = Ln (A2) - E2/RT
There are many other equations that try to get all the data in one equation, but the results are about the same.
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Is there any chance for a metal hydride reaction to slow down over a specific temperature?
Hi.
As a general rule, increasing the temperature will increase the reaction rate (for exothermic and endothermic) reactions simply because it means more energy available in the system. However, if you have a reversible exothermic reaction, there's a range of temperatures where this might not be true.
Picture the reaction A+B⇌C+D (- ΔH)
The reaction rate (relativelly to A, for example) can be defined as: -rA= K1[A]^a[B]^b - K2[C]^c[D]^D
Both K1 and K2 values depend on the temperature (and the induvidual activation energies for the reactions). So, if for some temperature and concentration ranges, the term K2[C]^c[D]^D is bigger than K1[A]^a[B]^b, the reaction can even occur from the products to the reactants. The difference between the terms is an indication of the direction and rate.
A well known example is the reaction between hydrogen and nitrogen to make ammonia. Very slow at room temperature, increasing rate with rising temperature up to the point where the balance at equilibrium shifts back towards reactants.
So, study well the kinetics of your reaction and you be the judge of the possibility.
Hope this helps!
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Hello,
Happy new year. I'm working on the synthesis of polymers using ultrasound assisted approach.
My question is how is possible to study the reaction kinetics and thermodynamics ?
Thank you Dr. Peter Farrington and Dr. Md. Abdur Rahman for your useful suggestions.
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This question is a bit complicated, but I will try to summarize succintly:
I have reaction kinetics data (order of reaction, reaction rate constant, and activation energy) for the degradation reaction of single CdSe/CdS core/shell quantum dots in air. I would like to use this information to determine (a) specific chemical reaction(s) associated with the degradation process. The system is a CdS surface with oleic acid passivating ligands. The surface is (presumably) reacting with either oxygen or water in the air. Is there a software package that will allow me to model such a reaction? Do I need to find a theorist who can help?
Thanks for any suggestions!
Having the rate equation with parameter values, it seems that you want to describe the process course mathematically. At the beginning, you can try to use the shrinking core model. However, the degree of complexity will depend on the assumptions made. Regards,
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I would like to know if anyone knows how to plot the surface ([B] vs t vs k1/k2 ) as a numerical solution of the kinetic model of the mechanism A -> B -> C, specifically for the concentration profile of the intermediate specie [B], using any MATLAB ODE solver.
Hi Enmanuel Duarte, the ODE solver will return a solution set of data points from the universe of discourse. So I think, at most, you can only get the 3-D line plot, not the surface, unless you want to obtain the slope field.
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I wanted to do a pH-stat experiment for lipase reaction kinetics, but I am finding the auto-titrators with pH-stat capabilities exceedingly expensive (~ 10000\$? , I also take suggestions on more affordable models) .
I have been thinking of building my own using an Arduino (or similar) together with kits from Atlas scientific, but I am afraid that the flow rates for their pump kit might be to high for the pH-stat type experiments. Anyone on RG that has successfully built such a device?
Why not use a pH-meter with pH stat capability and connect that to some dosing pump?
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recently, I was trying to get a kinetic view of the reaction rate within the biofilm and on electrode surface.
Based on Nicholson's equation, k0 of a redox reaction on electrode surface could be calculated based on CV method, and the k0 will be in a unit of cm/s.
But for the biofilm, I read some papers using Raman spectroscopy to determine the rate constant and they get an apparent rate constant in the unit of s-1. see the attached paper.
My question is is there any equation to convert the unit from s-1 to cm/s? or another way to compare the flux (mmol/cm2/s) across the biofilm and electrode surface?
Hi, Chaker,
Sorry, I cannot remember which paper it refers to. I probably renamed the file already when I downloaded it and it is not possible to trace it back.
Cheers, Bin
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In order to calculate the equilibrium pressure in the reaction kinetics for hydrogen storage in hydrides. I've found in letterature a polynomial expression of it in terms of (H/M) or (X). Please who can help me in this issue? So, I'm looking for the expression of (H/M).
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I am designing a CSTR reactor for the cativa process using methanol carbonylation reaction to methyl formate/acetic acid but unable to find the rate determining step for the methanol carbonylation and reaction kinetic data. so, i m unable to design reactor. If anyone has kinetic data so kindly share with me.
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I am designing a CSTR reactor for the cativa process using methanol carbonylation reaction to methyl formate/acetic acid but unable to find the rate determining step for the methanol carbonylation and reaction kinetic data. so, i m unable to design reactor. If anyone has kinetic data so kindly share with me.
The preferred industrial method for its manufacture is by the carbonylation of methanol and this accounts for approximately 60 per cent of the total world acetic acid manufacturing capacity. The carbonylation of methanol, catalysed by rhodium, was invented by Monsanto in the 1960s and for 25 years was the leading technology. In 1996 a new, more efficient, process for the carbonylation of methanol was announced by BP Chemicals, this time using an iridium catalyst. This article describes the new process and looks at the ways in which it improves upon the prior technology..
The apparatus of the present invention is used in connection with the carbonylation of methanol, and/or its reactive derivatives, with carbon monoxide in a homogeneous catalytic reaction system comprising a reaction solvent (typicallyacetic acid), methanol and/or its reactive derivatives, a soluble rhodium catalyst .
A process as provided for producing an acetic acid process stream having less than 400 ppm propionic acid and less than 1500 ppm water. Methanol or a reactive derivative thereof and carbon monoxide is fed to a carbonylation reactor in which there is maintained during the course of the process a liquid reaction composition containing an iridium carbonylation catalyst, methyl iodide co-catalyst, a promoter, water at a concentration of less than about 8% by weight, methyl acetate, acetic acid, and propionic acid by-product and its precursors. Liquid reaction composition is withdrawn from the carbonylation reactor and introduced to a flash zone to form a vapor fraction comprising water, acetic acid product, propionic acid by-product, methyl acetate, methyl iodide and propionic acid precursors, and a liquid fraction comprising involatile iridium catalyst, involatile optional promoter or promoters, acetic acid and water. The liquid fraction is recycled from the flash zone to the carbonylation reactor and introduced into a first distillation zone where a light ends recycle stream is removed and recycled to the carbonylation reactor, A process stream is removed from the first distillation zone comprising acetic acid, propionic acid by-product and less than 1500 ppm water. If the process stream comprises greater than 400 ppm propionic acid, the process stream is introduced into a second distillation zone where propionic acid by-product is removed together with an acetic acid process stream containing less than 400 ppm propionic acid and less than 1500 ppm water.
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I want to get the Km and Kcat of enzyme E3.
However its substrate C is very unstable for its R-S conformation exchange.
In order to measure the kinetics of one enzyme in a sequence of enzyme reactions, there are 2 necessary conditions I can think of.
(1) The reaction of the enzyme of interest has to be rate limiting (i.e. the slowest step). This can be achieved by keeping the concentrations of all the other enzymes very high. The test for this condition having been successfully achieved is that further increasing the concentrations of the other enzymes does not increase the rate of the E3 reaction.
(2) You have to know the concentration of the substrate of E3. This is challenging, but the way to do it is to run the reactions of E1 and E2 first with a known concentration of the substrate of E1, such that all of the E1 substrate is converted to the E3 substrate prior to the addition of E3. (This requires that the E1 and E2 reactions are essentially irreversible, otherwise the reaction will not go to completion.) Thus, the concentration of E3 substrate is equal to the input concentration of E1 substrate. I don't think you can run all the reaction concurrently and still be able to measure the kinetic constants for E3 because the concentration of the E3 substrate would be unknown. So substance C has to be stable for the amount of time needed for its formation to be completed.
You also have to measure the initial rate of E3 substrate consumption or product formation, as you would for any kinetics study. It isn't clear to me whether it is necessary for the D to E conversion step to be present in your scheme. If so, then the concentration of E4 (you labeled it E1) must also be high enough that the E3 reaction is rate limiting. You would then have to measure the rate of substrate C consumption or the rate of product E formation.
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I have found the following rate kinetics for the following reaction. As you see, the reaction is reversible one in which Xylene disproportionates and toluene and trimethylbenzene form ( r is reaction rate for xylene ).
If in the reactor, the reaction occurs in reverse direction such as toluene and TMB react and form Xylene, is it possible to use the same rate kinetics? Should I change some parameters? or this rate is OK for both reaction's direction?
( work done by André Luís Alberton )
The rates of individual reactions (forward and backward) are of course different (omitting state of equlibrium). It should remain unchanged the form of a kinetic equation, but one must remember to change the values of reaction rate constants (one on the other) or about changing the rate constant and equilibrium constant values. The problem may also occur if in the kinetic equation there will be pressure activities instead of partial pressures.
Yes, the above kinetic equation does not make sense unless we know the value of equlibrium partial pressure of benzene and the value of the constant KB has been adapted to this situation. Regards,
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Hello everyone,
I aim to insert reaction kinetics in a stripping column (RadFrac) I'm currently working at. My problem is the kinetic model I would like to implement uses rate constants which are not fitted with the temperature, as usual, but instead they use pH. For instance, an expression of this kind:
k = a + b*pH + c*pH^2
How could I overcome this difficulty?
Thank you very much.
Hi Enrique!
Perhaps you can use a Calculator Block. This tool of Aspen Plus will allow you to do a program with Import Variables (such as pH) and Export Variables (such as k) and to link them with different units operations, for example, a RadFrac Column.
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I need the dimensions of tatoray reactor such as diameter, height and so on. Could you please provide me with related information. Thank you in advance.
Teperatue rise depends on feed quality but typical conditions are 360 C inlet and 380 C outlet
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We are doing polymerization reactions with Salen Mn and Zn diketiminate complexes, working on reaction kinetics.
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Hi,
I have a question regarding modified Arrhenius equation:
k=ATbexp−E/RT
Does anyone knows how to choose the term temperature exponent 'b' for a specific reaction. The only thing I can find in literature is that it is often taken zero. But I can see it has effect on reaction results but could not find any literature to see how to choose it.
Dear Shahid,
By putting b to zero, you simply degenerate the modified Arrhenius to Arrhenius equation. The temperature dependency of the exponential factor is to give a better fit to an experimental observation. In that case it can be determined by fitting the equation to the experimental data.
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I want to reduce NaBO2 to NaBH4 on a catalyst (electrode). Kindly provide me suggestions of how can I confirm that the reduction of NaBO2 to NaBH4 is taking place or not?
IR. Peaks around 2300-2400 cm-1 can't be confused with much else. not the best technique for aqueous solution though, you;d have to isolate and dry. Raman better for aqueous solution, A1 totally symmetric BH4 str breathing mode at 2310 cm-1. such peaks provide positive fully diagnostic evidence.
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I have worked on Kinetic parameters of rechargeable Nickel Metal-hydride batteries and i have had a question about Avrami kinetic models,
In constant voltage discharge of a cell, if the shape of the curve looks like diffusion control models and the value of "n" in Avarami model is equal to 1, how can we analyze the results? does it mean diffusion of the reaction species control the reaction kinetic? Best Regards
Are you really interested in answering the question, because I have doubts. However, if I am wrong, answer the following questions please. What is a dependent variable? Is there an inflection point on the kinetic curve? Is the equation you use for the kinetic curve approximation to be y = exp (-atn+1) or y = exp (-atn)? What is the value of the coefficient a? Regards,
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I would like to find a conclusive research paper(s) which details all the reaction rate constants for the Cativa process / methanol carbonylation in a table.
I have looked through this paper:
Promotion of Iridium-Catalyzed Methanol Carbonylation:  Mechanistic Studies of the Cativa Process
However it does not seem to provide all the rate constants.
Any help much appreciated!
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While studying the effect of residence time on reactants conversion to product, it was noticed that after some time the conversion is no longer increasing, but remain almost stable. Generally, it is known that reaction rate decrease with time, but this may not be a sufficient reason for the observed trend. Kinetically/mass transfer limited phenomenon may not also apply here considering that the reaction is kinetically limited in the initial stage, so in theory it can not change to mass transfer later on. A possible reason but not sure about is that the reaction order or mechanism could change after sometime.
Where it is not known what the reaction is, under what conditions it occures, no relible answer is possible. The rate of chemical reaction can decrease with time, it can also increase and then decrease (autocatalitic reaction). There is also no the relationship between the order of chemical reaction and the behavior observed - no conversion changes. And I will repeat, I do not know. which once - the term "reaction order" refers to a single chemical reaction.
Or maybe the answer is the most trivial, that is, total consumption of the substrate. Regards,
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Why the first order kinetics used in polyphenol degradation, despite the fact that in some cases the decrease of concentration is linear?
Could the discussion be over?
The reaction (process) order is primarily the result of an experiment - correct experiment, but also a mathematical description. The situation you write is possible. This depends on the range of the change in initial substrate concentration. This type of behavior can also be described using hyperbolic functions, eg well-known equations as M-M or Monod (the same mathematically). Then for low concentrations the reaction may be considered as first order and for large as zero order. As low and large, the value of Km (Ks) is decisive . However, in the whole range of initial concentration change, the reaction (process) has no order (the definition of the reaction order), which is worth remembering. Regards,
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I had measured the CV of 0.1 M aniline in 1 M perchloric acid and I have got CV which I am going to attach from this file but the whole scenario is not clear to me about this CV what information from the peaks we are getting please elaborate if any body is familiar with this...
1. I want to know about every peaks.
2. reaction kinetics.
You have so high concentration of aniline that you possibly see the CV of impurities in aniline. CV is usually taken at concentrations around 1 mM
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Hi
if anyone has worked on modeling of Thermochemical heat storage by metallic oxides, please contact. i need help for modeling reaction kinetics of a reversible redox reaction. Its urgent. Thanks alot..!
Hi Mariam, How are you doing? Sorry I am busy these days working on some projects with immediate deadline. I went through the paper you attached to your previous message. There are some inconsistencies in that model
- first you should make sure if the enthalpy change of the reaction is in kJ/ mol O2 or kJ/mol Co3O4. Because kJ/mol O2=2 times kJ/mol Co3O4.
-second, in the kinetic model the effect of oxygen pressure is not given, which make the model wrong and may result in strange result.
To correct that calculate the equilibrium pressure of Oxygen as Peq=P0*exp(A-dH/(Rg*T)) where P0 is 1bar, Rg=8.314  dH the entalpy change of the reaction.
you can estimate A by knowing that Peq=1bar at 1164 K.
Then the reaction kinetics will be Rco3o4=Rred*X*(Peq-P)/Peq , Rred is given in your Word document. you should drop Rox because is significant low (tends to zero), P is the exit pressure of O2 and should be less than Peq. in simulation you can choose value less than 1 bar. the initial condition is X=1 at t=0.
Then your source term Sh=dH(in kJ/mol Co3O4)*Rco3o4*rho Co3O4/MW Co3O4
with  the unit of W/m3 to be consistent with the energy balance.
where rho Co3O4 is the bulk density of Co3O4 and MW Co3O4 is the molecular weight of Co3O4.
With all these suggestions in mind, your simulation will run perfectly. I hope it will help. Good work
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usually in calculating first and second order kinetics, we use the value of concentration. but if i want to calculate the reaction kinetics by using using flourescence intensity, what will be the equation?
If fluorescence intensity linearly depends on the conversion degree of reaction, then this is possible. However, you must remember that in the case of the first order reaction with the kinetic equation: r = kcA, the degree of conversion does not depend on the initial concentration of the substrate A, but in the case of the second order reaction with the kinetic equations: r = kcA2,r r = kcAcB etc. depends. You do not know, however, before the experiment, what the reaction order is, and therefore you need to perform the experiment with several initial substrate concentrations.
Of course, there will be no problem linking the intensity of fluorescence to the conversion degree for reaction A -> B. The value of the reaction rate constant will be different from that based on concentration measurement. Difficulties may occur, however, with bimolecular reaction and then better measure the concentration.
And finally, I intetionally used the term reaction order instead of kinetic order because this is correct.
Regards,
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A solution of A is mixed with an equal volume of solution B containing the same number of moles and the reaction A + B ↔ C occurs. At the end of 1 hour A is 75% reacted. How much of A will be left un-reacted at the end of 2 hours if the reaction is first-order in A and zero order in B?
We have been supplied the standard first order rate equation.
I am moderately familiar with enzyme kinetics. I understand this is a simple matter of using the formula, however I cannot for the life of me figure it out. Step by step details of how each part of the question is worked out, and why it is done that way, would be absolutely amazing!
Thank you,
Jack
You have written it as a reversible reaction implying that the forward rate slows down as the reaction approaches equilibrium. You didn't give enough data to compute the equilibrium constant. Zero order in B is not satisfactory for equal number of moles in a reversible reaction. Something is wrong in the statement.
Example as written a deficiency of B would not prevent A from becoming C. Other example a great excess of B would tend to make it zero order in B. Third example C might regenerate B spontaneously in which the reaction is written incompletely.
In your writing about enzymes they are catalysts which favors my third example where B is the enzyme a catalyst and hence a zero order participant.
A + B <--> C --> D + B
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I am having trouble working out the basics of enzymes kinetics. I understand the formulas, and what they mean, however applying data to the equations and returning a meaningful answer is something I'm struggling with. Here's an example of a question I can't figure out:
A solution of A is mixed with an equal volume of solution B containing the same number of moles and the reaction A + B ↔ C occurs. At the end of 1 hour A is 75% reacted. How much of A will be left un-reacted at the end of 2 hours if the reaction is:
A) First order in Both A and B
B) Zero order in both A and B
For instance, I know the answer to B) should be zero are changing, as it is relative on the concentration of the enzyme. I have figured this out from notes, however I don't quite understand it
If someone could explain how to apply the basic rate equation formulas to this question, and why you do what etc, i'd greatly appreciate it.
Thank you all for you your time :)
Hi there,
first order rate means velocity is directly proportional to reactant concentration:
v=k[A][B] and v may be expressed as v=-d[A]/dt. If considering the case where A and B are identical
v=-d[A]/dt=k[A]2 which leads to 1/[A] - 1/[A]0 = kt
in your case if t=1h, [A]=1/4 and [A]0=1, you can calculate k (k will be 3 h-1) and then knowing k apply the same equation at t=2h to get residual [A] (it will be 1/7)
If zero order, v is independent on reactant concentration v=-dA/dt and v=k so
[A]-[A]0=-kt. It is only observed for enzyme catalyzed reaction at saturating concentration of substrates and v depends only on enzyme concentration. So in your case, if A is 1/4 after 1h then k is 3/4 h-1.  So having consumed 3/4 of A in 1 hour and having v=k on the second hour it would mean that A would be fully consumed within this second hour (from the calculation A would be negative after 2h which can't occur...). In practicals zero order reaction couldn't be maintained during the whole reaction as at some point A and B would become limiting.
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Probable major and minor product and suitable reagent and catalyst for chlorination of the 2,5 dimethoxy amphetamine  .
Kind of controversial topic
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In estimation of total phenol and flavnoids per eg.
If Conc . 1000 (mg/l)  Abs 1.2
Then If conc. 500(mg/l) Abs. 0.6? Is that compulsory?
If the concentration is half then Absorbance should be half?
In many research articles it does not follow this trend.. There is decrements in absorbance ,but it is not directly proportional.
So how should be the actual curve for total phenols and flavnoids
if you are following proper method and  suitable wavelength, your absorbance is always proportional to your concentration.you should prepare lower concentration standards like 10ppm,20 ppm,30 ppm,40ppm and 50 ppm, dilute your sample as per required, keep your uv-vis absorbance< 1.0 AU.
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Greetings,
I have questions about the units for DR and Temkin Isotherms. I read a couple articles and I don't find a consensus about the units, especially for qt and Ce. I believe that the unit for Ce on Temkin Isotherms need to be L g-1 because of "k" (I found many authors saying that unit for "k" for Temkin is g L-1), but the units for qt it's a little bit vague for me (Needs to be mg L-1 because all my isotherm and kinetic studies use mg L-1, or they are models with different qt units?).
Thank you so much
If you study equilibrium of sorption (liquid-solid system) you are looking for the relationship between qe and Ce. If you study the kinetics, you determine experimentally the relationship between q and t (usually denoted in short qt) and then (by modeling) between r (rate) and q. The unit of variables in the model (and associated with them  values) depend solely on you. For Ce can be both g/L and g/m3. What will change - only the value of model parameters and their units.
Regards,
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I have a reaction(bi-molecular) for which I have formed reaction complex, transition state and product. Now I want to calculate the rate constant for the reaction as well as the quantity of the product forms (I know the Initial amount of the reactants). I have performed all the calculations using Gaussian 09 program.
Dear Keshav,
For pure bimolecular reactions, transition state theory (TST) would probably be a better approach. RRKM theory only applies to unimolecular reactions. If the reaction mechanism involves a bimolecular collision activation step followed by a unimolecular rate-determining step, RRKM theory can apply. But it doesn't seem to apply to the case described here.
Hope this helps.
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Working on designing the Cativa process but can not figure out the kinetics, really would appreciate the help.
Dear Elizabeth,
Have you found the pre exponential factor?
If yes could you please share it with me?
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Actually trying to model reaction kinetics of polyethylene in RCSTR, but have been having mass balance error. Really do not know what to do.
You may also check the molecular weights of the species involved (in the database), as Aspen databank components data are sometimes slightly different from the data you have from literature. Then manually check the balance using the values you retrieved from the database.
Do you have recycle streams in your process? Sometimes when you have recycle you need to ask to reconcile the streams.
Another thing to do is to increase the acceptable range of error. (Simulation – Setup- Calculation Options- Check results).
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HCL + NaOH
Thanks, Michael. For a long time I'm wondering what reaction rate constants should be assigned for the equilibrium H+ + HO- = H2O? This question might be worthy to discuss separately.
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We are analyzing an exothermic reaction that deals with the addition of mCPBA. But during addition, it yields an endothermic curve, followed by exothermic curve.
However when we take the conversion values with respect to addition, we obtain negative conversion values for the addition of mCPBA. We obtain positive conversion values After the addition of mCPBA.
As per the normal scenario we used to obtain positive  conversion values for an exothermic reaction when the heat generates, thermal conversion happens.
I need some suggestions on how to incorporate that negative conversion values in my calculations. Please refer to attachments.
Our article just accepted yesterday for publication in PCCP  may help you. The article is titled "Kinetic Analysis of Overlapping Multistep Thermal Decomposition Comprising Exothermic and Endothermic Processes: Thermolysis of Ammonium Dinitramide".
DOI: 10.1039/C6CP08218A
For the case of perfectly overlapping exothermic and endothermic processes, you can see the following our article in JPC C.
DOI: 10.1021/acs.jpca.5b07044
Similar kinetic treatment is required for the case of overlapping mass loss and mass gain process when tracking of kintiec rate data using TG. The example  for the successive thermal decomposition and oxidation of tin(II) oxyhydorxide has been published in JPC C.
DOI: 10.1021/acs.jpcc.5b04975
I am very glad if this information is useful for you.
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I obtained the heat generation data (Qrx) from RC1e Mettler Toledo with the integration with respect to baseline and reaction limits.
I extracted the individual thermo-kinetics data with time variation of two seconds, but we used an approach (refer attachment) to match the Qrx value of all the time intervals to the RC1e given Qrx and, we tried to plot the Qrx value of Excel, with respect to time but we are not obtaining the exact curve given by Mettler Toledo RC1e.
Can anyone  suggest to me how to find the calculation (Qrx) of integration and how to obtain the Qrx curve as similar to RC1e Qr curve?
It is difficult to answer without any explanation of the columns in your Excel file, or of how is your symbols are related to these data (i.e. which columns are realed to Qr or Qrx, what do these symbols stand for etc.), and what is exactly that you want to integrate or to plot. If you'll provide this information the probability of getting useful answers will be increased.
Also tell, do you really want to make the plots in Excel, or in some other environment.
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I have extracted some kinetics data Reaction calorimeter RC1e, and as I know the reaction rate,order,rate constant I can evaluate the total energy generation, corresponding to that I can estimate cooling capacity required?
But I was in a confusion, which reactor I should recommend to plant scale up.
As per my knowledge, I always recommend semi-Batch reactor because we can control the heat generation with the dosing, so we can escape thermal runaway scenario.A rational choice between a variety of  requires knowledge of reaction kinetics,thermodynamics and property of the reaction mixture through out the system.
Thus anyone please give me a proper clarification regarding aforementioned aspects.
"The choice of a suitable reactor for the chemical process depends on: the type of the reaction/reactions (rate, yield selectivity), type of substrates, type of products, the thermal effects, the ways  of heat exchange, production volume, catalyst used, accompaniing effects as phase transition, inter and intra particle diffusion, inter and intraparticle heat transfer etc etc, etc."
This phrase can be found in any book on chemical reactor engineering.
You wrote that you know (you know, not me) heat of reaction, estimated cooling capacity and, I guess, the kinetic equation.
It's not enough to propose the correct solution.
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Dear sir,
We are performing a reaction which involves nitration of 4-Hydroxy-2-trifluoromethyl pyridine in the Conc.sulfuric acid medium& fuming nitric acid added successively at 0°C and heated to 80°C to form compound 2-nitro-4-trifluoromethyl-phenol.
For the scheme please refer to attachment "kinetics.png".
I have completed with finding the rate constant and reaction order,However I am not able to estimate Enthalpy  of the reaction(-ΔHr) to find the total heat production or heat generation as mentioned in the equations below.
I have extracted the data from Mettler toledo RC1e, and I would like to mention that I had summed up the individual Qr,so i got the heat generation in the Watts(W), and I multiplied that total watts with the corresponding time to convert into Kilo-joules.
The total heat generated Qrx (kilo-joules) is not matching with the Corresponding RC1e Heat generation value.
And I want to plot those individual qr values w.r.t time to generate Qrx vs time Curve.
Further I would like to request from you any other similar case study which you can share.
Please refer to the excel sheet and final report attached for further clarification.
Kind Regards,
Raghu Perumalla,
Process Safety Engineer,
Scale Up Facility,
TCG Lifesciences Pvt Ltd,
Kolkata,India.
Arjun Chaudhuri,
M.Sc ( Bio Chemical Engineering )
Technical University of Delft,
The Netherlands.
Dear Raghavandra,  If I understand your question correctly you have used the Mettler RC1 to accurately record temperature rise as a function of time and calculate the amount of heat required for that temperature rise to occur and this does not match the calculated heat of reaction (Qrx) from literature similar to the source Prof Khalil sited.  The first thing to do is recheck the literature to make sure you understand the heat of reaction correctly.  Also you should make sure that you are looking at both the literature and experimental values properly and that you are accounting for any vaporization that may also be occurring as the process temperature rises.  The impact of heat of vaporization could potentially be large.  I hope this helps.
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The kinetics of reduction can be expressed by Arrhenius equation:
r=kexp(-E/RT) [CH4] , mol/m3.s
I am interested to know the kinetics parameters of K and E for the reduction of iron oxides with methane for mathematical simulations.
Here is a paper that explains reduction of Iron via partially oxidized methane the CO and H2 formed are the actual reducing agent.   Exxon had a large project to demonstrate this technology called the FeOR project back in the late 70's I was not directly involved but I knew several people who were. It was a technical success but an economic failure as I recall
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Dear all.
I have some confusion, I read an article talk about the effects of nostoichimetric on catalytic activity of La0.9MnO3
the auther explan the increase of catalytic activity of LaMnO3 with increasing of Mn content (La0.9MnO3) (for NO oxidation) is due to increase of Mn4+/Mn3+ ratio
while another investigation deduced that the catalytic activity of LaMnO3 ( LaMn0.9O3 ) (for methane combustion) is increase with increasing of La content
my question is how to explan the increase of catalytic activity with increasing of La content ?
Dear
Jerry Decker, Narjes
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VO+ 1/2 O2 gives VO2.  I need to find out the log K of this reaction?. Can someone help?
Dear Michael, I agree with all you posts.
You are right that
"VO + 1/2 O2 ↔ VO2 and K=(pO2)-1/2 as the standard activities of pure solids are 1 (and unitless)"
"use ΔRGϴ= - RT ln Kϴ".
My comment that " The equilibrium constants are not obligatory unitless" is also correct
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Hello how best would I electro-deposit ZnTe onto a metal Oxide with good adherence. Also the sulfuric acid used in dissolving the ZnTe seems to etch of the ITO glass substrate during deposition. How best can I do this deposition without etching the substrate as well