Question

The reaction

A(aq) + B(aq) → Products(aq)

was studied, and the following data were obtained:

[A]0 (mol/L)	[B]0 (mol/L)	Initial rate (mol/L•s)
0.16	0.24	3.76×10-2
0.080	0.16	1.25×10-2
0.040	0.12	4.70×10-3
0.32	0.12	3.76×10-2

The order of the reaction in A is _____.

Answer 1

rate = k [A]^m[B]ⁿ   , k = rate constant , m = order w.r.t A , n = order w.r.t B

To determine order of the reaction w.r.t A , we will keep the concentration of B constant and vary [A]   

rate₁ = k [A]₁^m[B]ⁿ ...1) for rate₁ = 4.70X10^-3   , [A]₁ = 0.040M , [B] = 0.12M

rate₂ = k [A]₂^m[B]ⁿ ....2)   for rate₂ = 3.76X10^-2 , [A]₁ = 0.32M , [B] = 0.12M

Dividing 1 by 2

rate₁ = k [A]₁^m[B]ⁿ (k and [B] will cancel out from numerator and denominator) rate₂ = k [A]₂^m[B]ⁿ   

(4.70X10-3 )(3.76X10^-2)   = ([A]₁/[A]₂)^m = (0.040/0.32)^m

0.125 = 0.125^m

so, m = 1

Order of the reaction with respect to A is 1