Question

The reaction \[\ce{2A + B -> C + D}\] obeys the rate equation, Rate = k [A]² [B]^1/2. Find the order of this reaction when A is present in large excess.

Answer 1

The given reaction is \[\ce{2A + B -> C + D}\]

Rate = k [A]² [B]^1/2

Its concentration remains nearly constant during the reaction.

So, [A]² is treated as a constant, and the rate law simplifies to:

Rate = k′[B]^1/2

where k′ = k[A]²

Effective order of reaction (in the presence of a large excess of A) is `1/2` i.e., half order.

Only the exponent of B matters in this condition.