Chemistry Q57 – JEE-MAIN 2025

Home Chemistry Chemical KineticsQuestion #283

Consider the following statements related to temperature dependence of rate constants. Identify the correct statements. A. The Arrhenius equation holds true only for an elementary homogenous reaction. B. The unit of A is same as that of k in Arrhenius equation. C. At a given temperature, a low activation energy means a fast reaction. D. A and Ea as used in Arrhenius equation depend on temperature. E. When Ea

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RT, A and Ea become interdependent. Choose the correct answer from the options given below:

Clue 1 of 3: Understand the Arrhenius Equation

The Arrhenius equation describes how the rate constant of a chemical reaction varies with temperature.

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Ninja Strategy•Systematic Statement Evaluation

Evaluate each statement (A-E) individually for correctness based on the fundamental principles of chemical kinetics and the Arrhenius equation, then identify the option containing only the correct statements.

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Step 1: Evaluate Statement A✦ Active

The Arrhenius equation is an empirical relationship that describes the temperature dependence of reaction rates. It is applicable to a wide range of reactions, including both elementary and complex, homogeneous and heterogeneous reactions, not just elementary homogeneous ones. Therefore, statement A is incorrect.

Step 2: Evaluate Statements B and C○ Expand

From the Arrhenius equation, $k = A e^{- E_{a} / R T}$ . Since $e^{- E_{a} / R T}$ is a dimensionless quantity, the unit of the pre-exponential factor $A$ must be the same as the unit of the rate constant $k$ . Thus, statement B is correct.

For statement C, a lower activation energy ( $E_{a}$ ) at a given temperature ( $T$ ) means that the exponent $- E_{a} / R T$ becomes less negative (or more positive). This results in a larger value for $e^{- E_{a} / R T}$ , which in turn leads to a larger rate constant $k$ . A larger rate constant signifies a faster reaction. Thus, statement C is correct.

Step 3: Evaluate Statements D and E○ Expand

The Arrhenius parameters, $A$ (pre-exponential factor) and $E_{a}$ (activation energy), are generally considered to be temperature-independent constants over a limited temperature range for most practical applications. The rate constant $k$ depends on temperature, but $A$ and $E_{a}$ are typically assumed constant. Thus, statement D is incorrect.

The pre-exponential factor $A$ and activation energy $E_{a}$ are independent parameters determined experimentally. The condition $E_{a} ≫ R T$ does not make them interdependent. Thus, statement E is incorrect.

Based on the evaluation, only statements B and C are correct.

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Chemistry Question 57 – JEE-MAIN 2025

Clue 1 of 3: Understand the Arrhenius Equation

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