Question

Define order of a reaction.

Hint:

Remember: \[ \text{Rate}=k[A]^m[B]^n \] Then, \[ \text{Order}=m+n \] and \[ \text{Molecularity}=a+b \] Do not confuse order with molecularity. Order is determined experimentally, whereas molecularity is based on the reaction mechanism.

Answer 1

Step 1: Start from the rate law expression.
For a reaction $aA + bB \rightarrow$ Products, the experimentally determined rate law is Rate $= k[A]^m[B]^n$, where $k$ is the rate constant and $m$, $n$ are the individual orders with respect to each reactant.
Step 2: Define overall order of reaction.
The order of a reaction is the sum of the powers of the concentration terms in the experimentally determined rate equation. For Rate $= k[A]^m[B]^n$, overall order $= m + n$.
Step 3: Key features.
Order is always determined experimentally, never from the balanced chemical equation. It can be zero, integer, fractional, or negative. Example: Rate $= k[A]^2[B]$ gives overall order $= 2 + 1 = 3$.