Chemical Kinetics · Question 3

Consider a reaction A + R Product. The rate of this reaction is measured to be k[A][R]. At the start of the reaction, the concentration of R, [R]0, is 10-times the concentration of A, [A]0. The reaction can be considered to be a pseudo first order reaction with assumption that k[R] = k' is constant. Due to this assumption, the relative error (in %) in the rate when this reaction is 40 % complete, is . [k and k' represent corresponding rate constants]

Answer

4 to 4.25

Solution

Let [A]0 = a, [R]0 = 10a. At 40 % completion: [A] = 0.6a, [R] = 10a - 0.4a = 9.6a.

True rate = k(0.6a)(9.6a); assumed rate = k'(0.6a) = k(10a)(0.6a).

Relative error = 10 - 9.69.6 100 = 4.17 \%

Answer: 4.17