[kizzler85]

The following data have been obtained for the decomposition of N2O5(g) at 67 C according to the reaction:

2(N2O5)---->4(NO2,g)+(O2,g)

Determine the order of the reaction with respect to N2O5 and the rate constant.

t/min               0          1           2          3          4          5
[N2O5]/M       1.000    0.705    0.497    0.349    0.246    0.173



Well...I know the rate of reaction in accordance with the dissapearance of reactants:

 -v- = - d[N2O5]/dt

...but thats about it!

[Juan R.]

What happened to the stoichiometric coefficient of the reactant in the reaction rate 

[kizzler85]

ooops -v- = -1/2 d[N2O5]/dt

[Juan R.]

You have the rate law

d[N2O5]/dt = -2 k [N2O5]ⁿ = K [N2O5]ⁿ

Now you may try different orders n until you fit to the data. For instance, n=0 means that v would be constant and your data shows that v is not constant; then cannot be n=0. Try n=1, n=2, n=3...

For instance, for n=1 one obtains, integrating the rate law,

ln[N2O5] = ln[N2O5]₀ - Kt

this means that when you plot ln[N2O5] versus time you see a line with tangent -K if your reaction is first order.

For n=2 one obtains

1/[N2O5] = 1/[N2O5]₀ + Kt

this means that when you plot 1/[N2O5] versus time you see a line with tangent K if your reaction is second order.

And so on.