Law Of Mass Action - Practice Questions & MCQ

It was introduced by Guldberg and Waage. It states that “the rate at which a substance reacts is directly proportional to its activity and the rate at which substances react together is directly proportional to the product of their activity each raised to a power which is equal to the corresponding stoichiometric number the substance present in the chemical reaction".

Activity is generally represented in terms of concentration or pressure of species involved

If active masses of A, B, C and D be represented in terms of their concentrations [A], [B], [C] and [D] respectively, then:

Rate of reaction of A ∝ [A]^m

Rate of reaction of B ∝ [B]ⁿ

_R1 ∝ [A]^m [B]ⁿ = K₁ [A]^m[B]ⁿ

_R2 ∝ [C]^p [D]^q = K₂ [C]^p [D]^q

NOTE: For pure solids or pure liquids , activity is always unity (1) .