Chemical Kinetics - Result Question 42
####42. According to the Arrhenius equation,
(2016 Adv.)
(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
(c) higher the magnitude of activation energy, stronger is the temperature dependence of the rate constant
(d) the pre-exponential factor is a measure of the rate at which collisions occur, irrespective of their energy
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Answer:
Correct Answer: 42. (d)
Solution:
- Rate constant, $\quad k=A e^{-E _a / R T}$
where, $E _a=$ activation energy and $A=$ pre-exponential factor
(a) If $E _a$ is high, it means lower value of $k$ hence, slow reaction. Thus, incorrect.
(b ) On increasing temperature, molecules are raised to higher energy (greater than $E _a$ ), hence number of collisions increases. Thus, correct.
(c) $\log k=\log A-\frac{E _a}{R T} \Rightarrow \frac{d(\log k)}{d T}=\frac{E _a}{R T^{2}}$
Thus, when $E _a$ is high, stronger is the temperature dependence of the rate constant. Thus, correct.
(d) Pre-exponential factor $(A)$ is a measure of rate at which collisions occur. Thus, correct.
