## A as pre-exponential factor

Arrhenius Equation: $\ln k = - \frac{E_{a}}{RT} + \ln A$

vincesmetona_3I
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### A as pre-exponential factor

Must the value of 'A' always given to us? And if not do we assume it is constant at different activation energies, temp., etc.?
Thanks

Cindy Chen_2I
Posts: 43
Joined: Wed Nov 18, 2015 3:00 am

### Re: A as pre-exponential factor

"A" would not be given if it cancels out. For example, when they ask you to calculate the relationship between two "k" at two different temperature, with the activation energy given, you can get the answer by using ln(k1/k2)= Ea/R*(1/T2-1/T1).

And yes, I believe in reality, the "A" would be different at different temperature and for different reactions.

604633468
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Re: A as pre-exponential factor

Yes, the value of A should always be given to you or is usually a constant for very small temperature change.