Chemistry Reaction Kinetics MDCAT 2019
PMDC Verified Question 52 of 80
If the energy of activation of a chemical reaction is very low, the rate of that chemical reaction is observed to be very high because?
A
Concentration of the reactants becomes irrelevant
B
Reaction proceeds without any transition state
C
Molecules of the reactants move slowly
D
Number of efficient or fruitful collisions increase
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Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Number of efficient or fruitful collisions increase
Concept:

The Arrhenius equation and collision theory dictate that rate depends on the frequency of effective (fruitful) collisions that overcome the activation energy barrier.

Formula:

$$ k = A e^{-E_a / RT} $$

Solution:

  • A very low activation energy (\( E_a \)) means the threshold energy required for a reaction is minimal.
  • Consequently, a much larger proportion of the colliding molecules will have enough kinetic energy to exceed this low barrier.
  • This drastically increases the number of fruitful collisions, making the reaction rate very high.


Why other options are incorrect:

Concentration always matters. A transition state always exists regardless of how low the energy is. Slow molecules would actually decrease the collision frequency.

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