JEE Advanced · 2016 · 22 May 2016 · Paper 1 · Chemical Kinetics

According to the Arrhenius equation,

(A)a high activation energy usually implies a fast reaction.
(B)rate constant increases with increase in temperature. This is due to a greater number of collisions whose energy exceeds the activation energy.✓ Correct
(C)higher the magnitude of activation energy, stronger is the temperature dependence of the rate constant.✓ Correct
(D)the pre-exponential factor is a measure of the rate at which collisions occur, irrespective of their energy.✓ Correct

Answer: (B), (C), (D)

Solution

The Arrhenius equation is

k = A e^{- E_{a} / R T}

. (A) is incorrect: high activation energy means fewer molecules have sufficient energy to react, so the reaction is slower. (B) is correct: increasing temperature increases the fraction of molecules with energy

\geq E_{a}

, thus increasing

k

. (C) is correct: the derivative

d (ln k) / d T = E_{a} / R T^{2}

shows that larger

E_{a}

gives stronger temperature dependence. (D) is correct: the pre-exponential factor

A

represents the frequency of collisions with proper orientation, independent of their energy.

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JEE Advanced · 2016 · 22 May 2016 · Paper 1 · Chemical Kinetics

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