Here’s a explanation of reaction order and molecularity:
1. Reaction Order
- Reaction order tells us how the rate of a reaction depends on the concentration of reactants.
- It is determined experimentally, not from the chemical equation.
- Each reactant has its own order, and the sum of these is the overall order of the reaction.
- For example, if a reaction is first-order in a reactant, doubling its concentration doubles the reaction rate; if it is second-order, doubling the concentration quadruples the rate.
Key point: Reaction order can be 0, 1, 2, fraction, or even negative, depending on how the reactant affects the rate.
2. Molecularity
- Molecularity refers to the number of reactant molecules that collide simultaneously to cause a reaction.
- It is a theoretical concept, based on the reaction mechanism.
- It can be:
- Unimolecular: one molecule reacts by itself.
- Bimolecular: two molecules collide and react.
- Termolecular: three molecules collide and react (rare).
Key difference:
- Reaction order is experimental and can be any number.
- Molecularity is theoretical and always a whole number (1, 2, or 3).