Chemical Kinetics and Nuclear ChemistryMedium

Question

Given below is an expression for the rate constant of a first-order reaction occurring at a certain temperature, T (K).

$$lnk = 14.34 - \frac{1.25 \times 10^{4}}{T}$$

The energy of activation in $kcal{mol}^{- 1}$ for the reaction is:

(Given: k in $s^{- 1},R = 1.987cal{mol}^{- 1}{\text{ }K}^{- 1}$ )

Options

A.24.84
B.14.34
C.18.63
D.12.42

Solution

Sol. [Key Concept: Arrhenius equation — rate constant and activation energy] From Arrhenius equation

$$\begin{matrix} & k = Ae^{\frac{- E_{a}}{RT}} \\ & lnk = lnA - \frac{E_{a}}{RT} \\ & \frac{E_{a}}{R} = 1.25 \times 10^{4} \\ & E_{a} = 1.25 \times 10^{4} \times 1.987 \\ & \ = 24.84kcal{\text{ }mol}^{- 1} \end{matrix}$$

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