# Following first order rxn

1. Feb 27, 2009

### atavistic

OK if we are given the following first order rxn:

$$2N_2O_5 - > 4NO_2 + O_2$$

The rate constant is $$k$$. Now how would we express the rate law for the decomposition of $$N_2O_5$$.

$$- d[N_2O_5]/dt = k[N_2O_5]$$

OR

$$- d[N_2O_5]/dt = 2k[N_2O_5]$$

I think it is the latter but I see all books use the former.zzz

Its urgent.

2. Feb 27, 2009

### Ygggdrasil

Re: Kinetics

Well, the rate is equal to -(1/2) d[N2O5]/dt. You cannot, however, say a priori that the reaction will be first order with respect to the concentration of N2O5 without knowing the reaction mechanism.