Question

Assertion (A): Rate of reaction increases with an increase in temperature.
Reason (R): Number of effective collisions decreases with an increase in temperature.

• 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:

Higher temperature $\to$ higher average kinetic energy $\to$ MORE effective collisions $\to$ faster reaction rate.

Answer 1

The Correct Option is C

Step 1: Evaluate the assertion using the Arrhenius equation.
From $k = Ae^{-E_a/RT}$, as temperature $T$ increases, the exponent $-E_a/RT$ becomes less negative, making $e^{-E_a/RT}$ larger and $k$ larger. Therefore, reaction rate increases with temperature. The assertion is true.
Step 2: Evaluate the reason using Maxwell-Boltzmann distribution.
At higher temperatures, the kinetic energy of molecules increases. The fraction of molecules with energy exceeding the activation energy $E_a$ becomes larger, not smaller.
Step 3: Conclude on effective collisions.
Effective collisions are those where reacting species possess energy $\geq E_a$ and correct orientation. With more molecules surpassing $E_a$ at higher temperature, the number of effective collisions per unit time increases. The reason states it decreases, which is false.
Step 4: Match to the correct option.
Assertion is true; Reason is false.
\[ \boxed{\text{A is true, R is false}} \]