Why reaction rate increases with temperature The observed increase in reaction rate with increasing temperature is primarily due to which factor?

Introduction / Context:
Temperature profoundly affects reaction rates. Understanding the mechanistic reason is essential for reactor design, safety, and scale-up, as temperature control directly influences productivity and selectivity.

Given Data / Assumptions:

• Molecules must possess energy equal to or greater than the activation energy Ea to react.
• Collisions must also be favorably oriented and sufficiently energetic—so-called effective collisions.

Concept / Approach:
With higher temperature, the Maxwell–Boltzmann distribution broadens and shifts, increasing the fraction of molecules with energies ≥ Ea. As a result, the frequency of effective collisions rises, increasing the rate constant per Arrhenius: k = A exp(−Ea/RT). Activation energy itself does not usually decrease with temperature; rather, more molecules surmount Ea.

Step-by-Step Solution:
As T increases, average kinetic energy increases.A larger fraction of collisions exceed Ea and are effective.Therefore, observed rate increases primarily because effective collision frequency increases.

Verification / Alternative check:
Arrhenius plots (ln k versus 1/T) exhibit a straight line with slope −Ea/R; as T rises, k increases exponentially, consistent with more effective collisions.

Why Other Options Are Wrong:

• (b) Activation energy is a property of the reaction path; it does not simply decrease with T.
• (c) While average kinetic energy increases, the key mechanistic statement is the increase in effective collisions; option (a) captures the collision–theory mechanism most directly.

Common Pitfalls:

• Confusing increased average kinetic energy with the specific concept of effective collisions leading to product formation.

Final Answer:
Increase in the number of effective collisions