Calculating the rate constant

Jan 2020
3
0
Glasgow
Hi Guys,
Ive got the following equation 2CH4 + O2 -> C2H4 + H2O. I need to find the rate constant, but don't know the activation energy so cant use the Arrhenius equation. I tried using the Eyring equation but dont have the values for the enthalpy and entropy of activation. Does anyone know how to solve this?

Thanks in advance
 
Jan 2020
3
0
Glasgow
Hi Guys,
Ive got the following equation 2CH4 + O2 -> C2H4 + H2O. I need to find the rate constant, but don't know the activation energy so cant use the Arrhenius equation. I tried using the Eyring equation but dont have the values for the enthalpy and entropy of activation. Does anyone know how to solve this?

Thanks in advance
In addition to this I know the reaction is running at 1073K.
 
Apr 2015
70
34
To obtain the rate constants for this reaction you need a mechanism because this is a catalysed reaction which leads to a multistep analysis.

I note that there have been several papers in the last 10 years, studying this reaction with different catalysts.
Unfortunately I no longer have access to the professional databases holding these papers so can only see the abstracts.

At a pinch you could try the simplest catalysed reaction sequence


\(\displaystyle C + R\mathop \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \limits_{{k_{ - 1}}}^{{k_1}} CR\mathop \to \limits^{{k_2}} C + P\)

Where C refers to the catalyst, R to the reactants and P to the products.

and


\(\displaystyle {K_s} = \frac{{{k_{ - 1}} + {k_2}}}{{{k_1}}}\)

is the Michaelis rate contant.

Edit, Dan can you help with the mathmL it doesn't seem to want to parse?react1.jpg
 
Last edited:
Jan 2020
3
0
Glasgow
To obtain the rate constants for this reaction you need a mechanism because this is a catalysed reaction which leads to a multistep analysis.

I note that there have been several papers in the last 10 years, studying this reaction with different catalysts.
Unfortunately I no longer have access to the professional databases holding these papers so can only see the abstracts.

At a pinch you could try the simplest catalysed reaction sequence


\(\displaystyle C + R\mathop \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over
{\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} \limits_{{k_{ - 1}}}^{{k_1}} CR\mathop \to \limits^{{k_2}} C + P\)

Where C refers to the catalyst, R to the reactants and P to the products.

and


\(\displaystyle {K_s} = \frac{{{k_{ - 1}} + {k_2}}}{{{k_1}}}\)

is the Michaelis rate contant.

Edit, Dan can you help with the mathmL it doesn't seem to want to parse?View attachment 318
Hi
Thank you for getting back to me. I hadn't considered Mechelis Menton. Ive rewritten K_s in terms of concentration as I dont have values for k1, k_-1 or k2 and got:
K_s = ([C]^3[P] [R]^2)/ [CR]^3 where [R] = [CH4]^2 [O2] and [P] = [C2H6] [H2O]^2
I am unsure how to work out the concentration of CR. Ill add in some numbers to explain my issue better.
If I have 1 mol of cataylst, 10 moles of CH4 and 5 moles of O2 per 1m^3, this gives the concentrations as [C]=1, [CH4] =10, [O2]=5. If 95% of the reactants are used up, then this means the outlet stream has the composition of the outlet as 1 mol Catalyst, 0.5 mol CH4, 0.25 mol O2, 4.75 mol C2H6 and 9.5 mol H2O. as the volume will still be one the conc of the product will be [4.75] [9.5]^2.
The only thing I need now is the concentration of CR, how do if calculate this as I dont have values for k1, k_-1 or k2?
 

topsquark

Forum Staff
Jul 2013
66
2
Any place where Alyson Hannigan can find me
I should probably update the LaTeX forum with this.

I had to look this up on the net. Most of the coding is simpler if you use certain packages but I don't know if we use any of them or not.

This is the basic element.
\(\displaystyle A \overset{U}{\underset{D} \rightleftarrows} X\)
A \overset{U}{\underset{D} \rightleftarrows} X

\(\displaystyle
C + R \overset{k_1} {\underset{k_{-1}} \rightleftarrows} CR \overset{k_1}{ \rightarrow} C + P
\)
C + R \overset{k_1} {\underset{k_{-1}} \rightleftarrows} CR \overset{k_1}{ \rightarrow} C + P

-Dan
 
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