Question

A reaction is first order in A and second order in B.

1. Write differential rate equation. 
2. How is the rate affected if the concentration of B is tripled? 
3. How is the rate affected if the concentrations of both A and B are doubled? 

A reaction is first order in A and second order in B.

1. Write the differential rate equation.
2. How is the rate affected on increasing the concentration of B three times?
3. How is the rate affected when the concentrations of both A and B are doubled?

Answer 1

i. The rate law is Rate = k[A]¹[B]²

ii. Let original rate be Rate₁ = [A][B]²

Now, if [B] is tripled:

Rate₂ ​= k[A](3[B])²

= k[A] × 9[B]²

= 9 × Rate_1​

Rate increases 9 times.

iii. If the concentrations of both A and B are doubled:

Rate2 ​= k(2[A])(2[B])²

= k × 2[A] × 4[B]²

= 8 × Rate₁​

The rate increases 8 times.