Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: kizzler85 on October 29, 2010, 08:15:30 PM
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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!
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What happened to the stoichiometric coefficient of the reactant in the reaction rate ???
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ooops -v- = -1/2 d[N2O5]/dt
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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.