Chemical reaction rate with ODE?

Hello im having some trouble solving a system of differential eqs. with ode45

The Chemical Reaction look like this

• A -> B+B (k1)
• B+C -> M (k2)
• B+D -> C (k3)

My function code

   function [f] = kinetic(t,Conc,R,K)

   k1=9.2*10^6*exp(108400/(R*K));
   k2=2.5*10^14*exp(244600/(R*K));
   k3=2.2*10^14*exp(317500/(R*K));

   f=zeros(length(Conc),1);
   f(1)=-k1*Conc(1);
   f(2)=k1*Conc(1)^2-k2*Conc(2)*Conc(3)-k3*Conc(2)*Conc(4);
   f(3)=-k2*Conc(2)*Conc(3)+k3*Conc(2)*Conc(4);
   f(4)=-k3*Conc(2)*Conc(4);

And the main script

   P=101325;
   R=8.314;
   K=1193;
   Conc=[A B C D] %The initial values of the concentrations

   [t, Conc]=ode45(@kinetic,[0:0.1:0.3],Conc,[],R,K);

When i run the script i get the following answer for

   Conc
    A       B       C       D
   NaN     NaN     NaN     NaN
   NaN     NaN     NaN     NaN
   NaN     NaN     NaN     NaN

What im i doing wrong?

[Marc]

Do you get an error from ode45? I assume you have defined the initial conditions.

[Jonas Hoen]

I dont get an error only the NaN [A B C D] is replaced by a calculated mol pr volume

This is the result i get

 Conc =

    0.5108         0    0.0020    0.5469
       NaN       NaN       NaN       NaN
       NaN       NaN       NaN       NaN
       NaN       NaN       NaN       NaN

Answer 1

[Youssef Khmou]

You did not mention the parameters A,B,C and D :

i tried with A=12.2;B=14.3;C=15.5;D=17.6; it gives :

Conc =

1.0e+030 *

    0.0000    0.0000    0.0000    0.0000
   -0.0000   -0.3894    0.4416   -0.4419
   -0.0000   -0.7788    0.8831   -0.8837
   -0.0000   -1.1683    1.3247   -1.3256

[Jonas Hoen]

If i insert the values in the function i get what u get but isnt the ODE function supposed to get the initial values from the script and not write it directly in the function?

Answer 2

[lisa]

I think the energy in the reaction rate expression should be negative, otherwise, the rate will be too large.