6. The rate constant for a certain chemical reaction is 71.0 s -1 at a temperatu
ID: 923223 • Letter: 6
Question
6. The rate constant for a certain chemical reaction is 71.0 s-1 at a temperature of 20.0°C. If the activation energy for this reaction is 52. kJ/mole, what is the rate constant at a temperature of 30.0°C?
7. A certain batch of fireflies were observed to "flash" at the rate of 18.7 times per minute at 25°C, and at the lower rate of 5.9 times a minute at a temperature of 15°C. Assume that the flashing is the result of an overall chemical reaction that has a single rate limiting step with the highest activation energy. Use this data to estimate the activation energy for this slowest step. You can assume that the concentrations of "reactants" in the fireflies do not depend on temperature.
Explanation / Answer
6)
k1 = 71 at T = 20 = 293
E = 52 kJ/mol
k2 = ? T2 = 30 = 303
Apply ahrrenius equation
ln(k2/k1) = -E/R*(1/T2-1/T1)
ln(k2/71) = -52000/8.314*(1/(303)-1/293)
k2/71 = exp(0.70450)
K2 = 71*exp(0.70450) = 143.6212
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