Question

A reaction is second order w.r.t. a reactant. How will the rate of reaction be affected if the concentration of the reactant is
(i) doubled
(ii) reduced to half

Answer 1

A reaction is second order w.r.t. a reactant. How will the rate of reaction be affected if the concentration of the reactant is
(i) doubled
(ii) reduced to half


Answer

Let the concentration of the reactant be [A] = a

Rate of reaction, R = k [A]2 = ka2

 

(i) If the concentration of the reactant is doubled, i.e. [A] = 2a, then the rate of the reaction would be

R = k(2a)2

= 4ka2

= 4 R

Therefore, the rate of the reaction would increase by 4 times.

 

(ii) If the concentration of the reactant is reduced to half, i.e. [A] = 1/2 a,then the rate of the reaction would be

R = k(1/2a)2

= 1/4 Ka2

= 1/4 R

Therefore, the rate of the reaction would be reduced to ¼th

Answer 2

Let concⁿ of reactant = n

=> Rate of rxⁿ = k[A]²=k[n]²

(i)If concⁿ is doubled , i.e, [A]=2n

R = k[2n]²

= 4kn²

Hence,the rate of rxⁿ increase 4times

(ii)If concⁿ is halved , i.e, [A]=½n

=> R= k[½n]²

= ¼kn²

Therefore, it becomes ¼th