Increasing temperature generally affects the rate of a reaction by

• A. Lowering activation energy.
• B. Increasing the fraction of molecules exceeding activation energy.
• C. Removing the need for a collision.
• D. Decreasing collision frequency.

Answer: (B)

Increasing temperature changes the distribution of molecular energies so that a larger fraction of molecules have enough energy to overcome the activation energy barrier. Because a reaction requires at least that energy in a collision to proceed, more energetic collisions mean more successful reactions and a faster rate. This idea is captured by the Arrhenius relation k = A exp(-Ea/RT): as T rises, the exponential factor increases, boosting the rate constant. The activation energy is not itself lowered by heating (that would be a change in the reaction pathway, not just temperature), and collisions are still needed—temperature generally increases both the energy of collisions and, to some extent, how often collisions occur, not eliminates the need for collision.