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Multiple Choice
Using the Arrhenius Equation, if the activation energy for a reaction is 80 kJ/mol, at what temperature will the rate be ten times faster than at 0 degrees Celsius?
A
Approximately 350 K
B
Approximately 298 K
C
Approximately 400 K
D
Approximately 500 K
Verified step by step guidance
1
Start by understanding the Arrhenius Equation: \( k = A e^{-\frac{E_a}{RT}} \), where \( k \) is the rate constant, \( A \) is the pre-exponential factor, \( E_a \) is the activation energy, \( R \) is the gas constant (8.314 J/mol·K), and \( T \) is the temperature in Kelvin.
Since the rate is ten times faster, the new rate constant \( k_2 \) is ten times the original rate constant \( k_1 \). Therefore, \( \frac{k_2}{k_1} = 10 \).
Use the ratio of the Arrhenius equations for the two temperatures: \( \frac{k_2}{k_1} = \frac{A e^{-\frac{E_a}{R T_2}}}{A e^{-\frac{E_a}{R T_1}}} = e^{-\frac{E_a}{R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right)} \).
Substitute \( \frac{k_2}{k_1} = 10 \), \( E_a = 80000 \) J/mol, \( R = 8.314 \) J/mol·K, and \( T_1 = 273 \) K (0 degrees Celsius) into the equation: \( 10 = e^{-\frac{80000}{8.314} \left( \frac{1}{T_2} - \frac{1}{273} \right)} \).
Solve for \( T_2 \) by taking the natural logarithm of both sides and rearranging the equation: \( \ln(10) = -\frac{80000}{8.314} \left( \frac{1}{T_2} - \frac{1}{273} \right) \). Calculate \( T_2 \) to find the temperature at which the rate is ten times faster.