Question

Which of the following is not correct about the order of a reaction?

• A. The order of a reaction is the sum of the powers of molar concentration of the reactants in the rate law expression.
• B. The order of reaction is always equal to the sum of the stoichiometric coefficient of reactants in the balanced chemical equation of a reaction.
• C. The order of a reaction can be a fractional number.
• D. Order of a reaction is an experimentally determined quantity.

Hint:

The order of a reaction is determined experimentally and is not necessarily related to the stoichiometric coefficients in the balanced chemical equation. It can be fractional or even zero for some reactions.

Answer 1

The Correct Option is B

Let’s evaluate each statement: - Statement (1): "The order of a reaction is the sum of the powers of molar concentration of the reactants in the rate law expression." This statement is correct. The order of a reaction is determined by the powers to which the concentration terms are raised in the rate law. The overall order is the sum of the individual exponents of the concentration terms of the reactants. - Statement (2): "The order of reaction is always equal to the sum of the stoichiometric coefficient of reactants in the balanced chemical equation of a reaction." This statement is incorrect. The order of a reaction is not necessarily equal to the sum of the stoichiometric coefficients in the balanced chemical equation. The order is an empirical quantity and is determined experimentally, often not matching the stoichiometric coefficients. For example, the rate law for a reaction may involve the concentration of a reactant raised to a power that is not equal to its stoichiometric coefficient. - Statement (3): "The order of a reaction can be a fractional number." This statement is correct. The order of a reaction can indeed be a fractional number. This occurs in cases where the reaction rate depends on the concentration of a reactant in a way that is not an integer, such as in complex reactions or elementary steps that are not whole-numbered. - Statement (4): "Order of a reaction is an experimentally determined quantity." This statement is correct. The order of a reaction is determined experimentally by measuring the concentration of reactants over time and analyzing the data to determine how the rate depends on the concentration.
Thus, the incorrect statement is Statement (2), as the order of a reaction is not always equal to the sum of the stoichiometric coefficients in the balanced chemical equation.