Question

Define order of a reaction.

Hint:

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

Answer 1

Step 1: Definition of Order of a Reaction.
The order of a reaction is the sum of the powers of the concentration terms in the rate law of the reaction. It indicates how the rate of reaction is affected by the concentration of reactants.

Step 2: Determining the Order of a Reaction.
The order is determined experimentally and can be a whole number, fraction, or even zero. The rate law for a reaction is generally written as:
\[ \text{Rate} = k[A]^m[B]^n \] where:
- \( k \) is the rate constant, 
- \( [A] \) and \( [B] \) are the concentrations of reactants, 
- \( m \) and \( n \) are the orders with respect to each reactant, 
The total order of the reaction is \( m + n \).

Step 3: Examples of Reaction Orders.
1. First-order reaction: If the rate law is \( \text{Rate} = k[A]^1 \), the reaction is first-order with respect to \( A \). 
2. Second-order reaction: If the rate law is \( \text{Rate} = k[A]^2 \), the reaction is second-order with respect to \( A \). 
3. Zero-order reaction: If the rate law is \( \text{Rate} = k \), the reaction is zero-order, meaning the rate is independent of the concentration of reactants.

Conclusion.
The order of a reaction reflects how the rate of reaction depends on the concentrations of reactants, and it is determined experimentally.