Question

State the difference between molecularity of a reaction and order of a reaction. Write the velocity equation for the reaction \( H_2(g) + Cl_2(g) \rightarrow 2HCl(g) \), which is a zero-order reaction.

Hint:

Molecularity applies to elementary reactions only, while order is determined experimentally for any reaction.

Answer 1

- Molecularity:
The number of reacting species involved in an elementary reaction. It is always a whole number.
- Order:
The sum of the powers of the concentration terms in the rate law. It can be fractional or zero. Velocity equation for zero-order reaction: \[ \text{Rate} = k \quad \text{(independent of reactant concentrations)}. \] For the reaction \( H_2 + Cl_2 \rightarrow 2HCl \), the rate equation is: \[ \text{Rate} = k. \]