Question

A reaction is of first order with respect to A and second order with respect to B.
(i) Write differential rate equation.
(ii) How is the rate affected when the concentration of B is trippled?
(iii) How is the rate affected when the concentration of both A and B is doubled.

Answer 1

(i) Rate of reaction
\(\frac { dx }{ dt } \) = k[A] [B]²

(ii) Let[A] = a, [B] = b
If [B] is increases three times
[B] = 3b
then,
rate = k[A] [B]²
rate₁ = k × a × b²          ….(1)
rate₂ = k x a x (3b)²        …(2)
from eq (1) and (2)

(rate)₂ = 9 x (rate)₁
The rate becomes nine times.

(iii) (rate) = k[A] [B]²
(rate)₁ = k x a x b²
(rate)₂ = k x (2a) x (2b)₂

(rate)2 = 8 (rate)₁
The rate becomes eight times.