The rate equation for a reaction mechanism is determined by the slowest step (the rate-determining step).
The given mechanism is:
- N2O5(g)→N2O3(g)+O2(g) (Slow step)
- N2O3(g)→NO(g)+NO2(g) (Fast step)
- NO(g)+N2O5(g)→3NO2(g) (Fast step)
The slow step is the first step:
N2O5(g)→N2O3(g)+O2(g)
For an elementary step, the rate law can be written directly from the stoichiometry of the reactants in that step. In this slow step, one molecule of N2O5 reacts.
Therefore, the rate equation for the reaction is:
Rate=k[N2O5]
The rate equation for the reaction is Rate=k[N2O5].