The rate of a reaction quadruples when temperature changes from to . Calculate the energy of activation.
Given
- A
- B
- C
- D
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Correct answer: A
To solve this problem, we will use the Arrhenius equation, which relates the rate constant ($k$) of a chemical reaction to the temperature ($T$) and the activation energy ($E_a$). The equation in its logarithmic form is:
where:
- $k$ is the rate constant,
- $A$ is the pre-exponential factor (frequency factor),
- $E_a$ is the activation energy,
- $R$ is the universal gas constant ($$8.314 \, \text{J mol}^{-1} \text{K}^{-1}$$),
- $T$ is the temperature in Kelvin,
- $2.303$ is the factor to convert from natural log to common log.
According to the problem, the rate of the reaction quadruples ($k_2 = 4k_1$) when the temperature increases from $27^{\circ}C$ (which equals $$27 + 273.15 = 300.15 \, K$$) to $57^{\circ}C$ (which equals $$57 + 273.15 = 330.15 \, K$$). Using the logarithmic form of the Arrhenius equation, for two different temperatures we have:
With $k_2 = 4k_1$, substituting in the values and taking their difference:
Given that $\log 4 = 0.6021$, we now solve for $E_a$:
First, calculate $$\frac{1}{300.15} - \frac{1}{330.15}$$:
So,
Solve for $E_a$:
Therefore, the activation energy $E_a$ is $$38.07 \, \text{kJ/mol}$$, which best matches Option A:
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