Question

The decomposition of gaseous ammoniaona hot platinum surface is a zero order reaction athigh pressure.Rate =k(a)what is the order of reaction.(b)give

Answer 1

Why is the decomposition of gaseous ammonia on a hot platinum surface a zero order reaction?

First of all, order of a reaction is an experimental concept and cannot be always predicted theoretically.

However, for the above mentioned reaction, it can be said that the Pt surface acts as a catalyst. At substantial pressure of gaseous NH3, all the free surfaces of Pt are occupied, hence the reaction rate is independent of concentration (or pressure) of NH3, implying a zero-order reaction. (According to Langmuir isotherm)

However, at very low pressure, the free sites of Pt are not fully occupied and the reaction will then be a first-order reaction.