Given the data below for the reaction, 2 A + 2 B + 4 C => D + E + 3 F, the reaction is ___________ order in A, ___________ order in B, _____________ order in C and ___________ order overall.

Question

Given the data below for the reaction, 2 A + 2 B + 4 C => D + E + 3 F, the reaction is _____________ order in A, _______________ order in B, ______________ order in C and ______________ order overall.

Experiment	Initial conc of A, mol/L	Initial conc of B, mol/L	Initial conc of C, mol/L	Initial rate, mol/L.s
1	0.1	0.2	0.4	2 x 10-3
2	0.2	0.2	0.4	2 x 10-3
3	0.3	0.4	0.4	8 x 10-3
4	0.4	0.6	0.2	9 x 10-3

answer for A: zero

answer for B: second

answer for C: first

Overall: third

Answer 1

For A, compare experiments 1 and 2 where A doubles and B and C are constant. Rate stays the same, so this is zero order in A

For B, compare experiments 2 and 3 where B doubles, C stays the same and A increases, but it doesn't matter because A has no effect on rate (it is zero order). The rate increases 4-fold, so it is second order in B. You could also compare experiments 1 and 3 where B doubles, C stays constant and A doubles (but again, it doesn't matter about A since it is zero order and has no effect on rate).

For C, compare experiments 2 and 4 (again, changing [A] is not relevant). In this comparison, [B] triples, so might expect rate to increase 9-fold b/c it is 2nd order in B. However, the [C] is halved (0.4 to 0.2), and the rate increases only 4.5-fold instead of the anticipated 9-fold. You might expect it to increase 9-fold if [C] remained at 0.4 M, but it was reduced to 0.2 M. This suggests first order in C.

Overall order = zero + 1 + 2 = third order overall.