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The activation energies of two reactions...

The activation energies of two reactions are `E_(1)` & `E_(2)` with `E_(1)gtE_(2)`. If temperature of reacting system is increased from `T_(1)` (rate constant are `k_(1)` and `k_(2)`) to `T_(2)` (rate constant are `k_(1)^(1)` and `k_(2)^(1)`) predict which of the following alternative is correct.

A

`(k_(1)^(1))/(k_(1))=(k_(2)^(1))/(k_(2))`

B

`(k_(1)^(1))/(k_(1))gt(k_(2)^(1))/(k_(2))`

C

`(k_(1)^(1))/(k_(1))lt(k_(2)^(1))/(k_(2))`

D

`k_(1)^(1)ltk_(2)^(1)`

Text Solution

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The correct Answer is:
To solve the problem, we need to analyze the effect of temperature on the rate constants of two reactions with different activation energies. Here’s a step-by-step solution: ### Step 1: Understand the Arrhenius Equation The Arrhenius equation relates the rate constant (k) of a reaction to its activation energy (Ea) and temperature (T): \[ k = A e^{-\frac{E_a}{RT}} \] where: - \( k \) = rate constant - \( A \) = pre-exponential factor - \( E_a \) = activation energy - \( R \) = universal gas constant - \( T \) = temperature in Kelvin ### Step 2: Write the Rate Constants for Two Temperatures For two reactions with activation energies \( E_1 \) and \( E_2 \) (where \( E_1 > E_2 \)), we can express the rate constants at two different temperatures \( T_1 \) and \( T_2 \): 1. For the first reaction: \[ k_1' = A_1 e^{-\frac{E_1}{RT_2}} \] \[ k_1 = A_1 e^{-\frac{E_1}{RT_1}} \] 2. For the second reaction: \[ k_2' = A_2 e^{-\frac{E_2}{RT_2}} \] \[ k_2 = A_2 e^{-\frac{E_2}{RT_1}} \] ### Step 3: Formulate the Ratios of Rate Constants We can form the ratios of the rate constants at the two temperatures: 1. For the first reaction: \[ \frac{k_1'}{k_1} = \frac{e^{-\frac{E_1}{RT_2}}}{e^{-\frac{E_1}{RT_1}}} = e^{-\frac{E_1}{RT_2} + \frac{E_1}{RT_1}} = e^{\frac{E_1}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right)} \] 2. For the second reaction: \[ \frac{k_2'}{k_2} = \frac{e^{-\frac{E_2}{RT_2}}}{e^{-\frac{E_2}{RT_1}}} = e^{-\frac{E_2}{RT_2} + \frac{E_2}{RT_1}} = e^{\frac{E_2}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right)} \] ### Step 4: Compare the Ratios Now we can compare the two ratios: \[ \frac{k_1'}{k_1} \text{ and } \frac{k_2'}{k_2} \] Taking the natural logarithm of both ratios: \[ \ln\left(\frac{k_1'}{k_1}\right) = \frac{E_1}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right) \] \[ \ln\left(\frac{k_2'}{k_2}\right) = \frac{E_2}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right) \] ### Step 5: Analyze the Effect of Activation Energies Since \( E_1 > E_2 \), it follows that: \[ \frac{E_1}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right) > \frac{E_2}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right) \] This indicates that: \[ \ln\left(\frac{k_1'}{k_1}\right) > \ln\left(\frac{k_2'}{k_2}\right) \] Thus, we conclude: \[ \frac{k_1'}{k_1} > \frac{k_2'}{k_2} \] ### Conclusion This means that the increase in the rate constant for the reaction with the higher activation energy \( E_1 \) is greater than that for the reaction with the lower activation energy \( E_2 \). ### Final Answer The correct alternative is that \( \frac{k_1'}{k_1} > \frac{k_2'}{k_2} \). ---

To solve the problem, we need to analyze the effect of temperature on the rate constants of two reactions with different activation energies. Here’s a step-by-step solution: ### Step 1: Understand the Arrhenius Equation The Arrhenius equation relates the rate constant (k) of a reaction to its activation energy (Ea) and temperature (T): \[ k = A e^{-\frac{E_a}{RT}} \] where: - \( k \) = rate constant - \( A \) = pre-exponential factor ...
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