COMEDK 2025 Morning Solved Paper

Concept:The Arrhenius equation explains why the rate constant $k$ roughly doubles per $10^\circ\mathrm{C}$ rise, mainly due to an exponential increase in the fraction of molecules with sufficient activation energy, not just due to increased collision frequency.Explanation:Assertion (A) is correct: As a rule of thumb, $k$ nearly doubles for every $10^\circ\mathrm{C}$ rise in temperature.Reason (R) is also correct: Higher temperature leads to faster molecular speeds and a greater number of bimolecular collisions.However, the primary cause of $k$ doubling is the exponential factor $e^{-E_a/(RT)}$ in the Arrhenius equation: $k = A e^{-E_a/(RT)}$.The fraction of molecules with energy above the activation barrier increases far more strongly with temperature than the collision frequency (which only scales as $\sqrt{T}$).Therefore, R is true but it does not correctly explain A; the true explanation is the exponential dependence on temperature in the Arrhenius equation.Answer:Option B: Both A and R are correct but R is not the correct explanation of A.