Question

Define order of a reaction.

Hint:

Order ≠ stoichiometric coefficient. It is determined experimentally from rate law.

Answer 1

Concept: In chemical kinetics, the rate of a reaction depends on the concentration of reactants. This dependence is expressed through the rate law. For a general reaction: \[ aA + bB \rightarrow \text{Products} \] Rate law: \[ \text{Rate} = k[A]^m[B]^n \]
Definition: The
order of a reaction is defined as the sum of the powers of the concentration terms appearing in the rate law. Mathematically: \[ \text{Order} = m + n \]
Types of order:

• Zero order → Rate independent of concentration
• First order → Rate depends on one reactant
• Second order → Sum of powers = 2
• Fractional order → Non-integer values possible

Important Note: Order is determined experimentally and may not match stoichiometric coefficients. \[ \therefore \text{Order = Sum of powers of concentration terms in rate law. \]