Which of the following statements is NOT correct regarding order of reaction?
- It is determined experimentally.
- It is not influenced by stoichiometric coefficient of reactants.
- It is sum of power to the concentration terms of reactants in rate law equation.
- It is always whole number.
Solution
The order of a reaction, an experimentally determined quantity, specifies how the rate depends on reactant concentrations.
A. The order must be determined experimentally, as it is not generally predictable from stoichiometric coefficients.
B. The stoichiometric coefficients do not influence the order, which may differ from them in complex reactions.
C. The overall order is the sum of the exponents on the concentration terms in the rate law: for $\text{Rate} = k[A]^x[B]^y$, it is $x + y$.
D. Orders are not necessarily whole numbers; they can be fractional, as in the $1.5$ order for acetaldehyde decomposition or the fractional order in $\text{H}_2 + \text{Br}_2 \rightarrow 2\text{HBr}$.
Only D is incorrect.
Asked in: MHT CET 2025 (05 May Shift 2)