Question

Assertion (A) : Order of reaction is not applicable for elementary reaction but applicable for complex reaction. Reason (R) : Order of reaction is an experimental quantity.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Molecularity is defined only for elementary reactions, whereas order of reaction is obtained experimentally and can be assigned to both elementary and complex reactions.

Answer 1

The Correct Option is D

Concept: In chemical kinetics, two important terms are:

• Order of reaction

• Molecularity of reaction
Although these terms may appear similar, they are fundamentally different concepts.

Step 1: Understanding order of reaction. Order of reaction is defined as the sum of the powers of concentration terms appearing in the experimentally determined rate law. For example, \[ \text{Rate}=k[A]^2[B] \] Order \[ =2+1=3 \] Order is determined experimentally.

Step 2: Understanding elementary reactions. For elementary reactions, the rate law can be written directly from the stoichiometric equation. Example: \[ A+B \rightarrow Products \] Rate: \[ =k[A][B] \] Therefore order is perfectly applicable to elementary reactions. Thus the Assertion is false.

Step 3: Examine the Reason. The statement that order of reaction is an experimental quantity is absolutely correct. The order cannot generally be predicted merely from the balanced equation and must be determined experimentally. Hence the Reason is true.

Step 4: Final conclusion. Assertion is false but Reason is true. \[ \boxed{\text{Option (D)}} \]