A2 + B + C → AC + AB, it is found that tripling the concentration of A2 triples the rate,

Question

For the reaction, 

A₂ + B + C → AC + AB, it is found that tripling the concentration of A₂ triples the rate, doubling the concentration of C doubles the rate and doubling the concentration of B has no effect,

(a) What is the rate law?

(b) Why the change in concentration of B has no effect?

Answer 1

Given,

A₂ + B + C → AC + AB

(a) The rate law may be represented as,

Rate = k [A₂]^x [B]^y[C]^z

Let [A]₁,[B]₁ and [C]₁ represent initial concentration and [A]₂,[B]₂ and [C]₂ represent final concentrations, and let R₁ and R₂ be initial and final rates of the reaction when the concentrations are changed.

(i) If [A]₂ = 3[A]₁, R₂ = 3R₁

If the concentrations of B and C remain constant, then

(b) In the rate determining step, B may not be involved as the reactant, hence rate is independent of changes in concentration of B. 

(OR B may be in large excess as compared to the concentrations of A and C.)