School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM330 – PHYSICAL CHEMISTRY
Chemical Kinetics Revision Exercises
Determination of reaction order
Use of integrated rate equations:
In a study of the reaction of pyridine with ethyl iodide,
C5H5N + C2H5I → C7H10N+ + Iˉ
the initial concentrations of both reactants were 0.10 mol dm-3. The concentration of iodide
ion was monitored at various times as follows:
t/s
[Iˉ]/mol dm-3
230
0.015
465
0.026
720
0.035
1040
0.044
1440
0.052
1920
0.059
2370
0.064
Determine the reaction order and the rate constant.
Method of half-lives:
For the thermal decomposition of N2O at 1030 K, the half-life, t½, was found to vary as
follows with the initial pressure, P0:
P0/Torr
t½/s
86.5
634
164
393
290
255
360
212
Deduce the order of the thermal decomposition of N2O.
Method of initial rates:
The reaction of nitric oxide with hydrogen,
2NO + 2H2 → N2 + 2H2O
has been studied by following the change in total pressure. At a fixed hydrogen pressure the
following rate data were obtained:
NO pressure/Torr
359
300
240
183
Initial rate/Torr s-1
1.50
1.03
0.64
0.37
Determine the order with respect to NO.