Sketch the reaction profile for a reaction having Ea = 50 kJ/mol and (change in)Hrxn = -75 kJ/mol. Suppose that in the presence of a catalyst the activation energy is reduced to 25 kJ/mol. Sketch the reaction profile of the catalyzed reaction on the same sketch you drew for the uncatalyzed reaction. Make sure to label each axis, (change in)H for the reaction, and Ea for the catalyzed and uncatalyzed reactions in both the forward and reverse directions.

Experiments have shown that the average frequency of chirping by a snowy tree cricket (Oecanthus fultoni) depends on temperature as shown in the table. Chirping Rate (per min) Temperature (C) 178 25.0 126 20.3 100. 17.3 What is the apparent activation energy of the process that controls the chirping? What is the rate of chirping expected at a temperature of 7.5C?

A catalyst reduces the activation energy of a reaction from 215 to 206 kJ. By what factor would you expect the reaction-rate constant to increase at 25 C? Assume that the pre-exponential term (A) is the same for both reactions. (Hint: Use the formula ln k = ln A Ea/RT.)

Experiments during a recent summer on a number of fireflies (small beetles, Lampyridaes photinus) showed that the average interval between flashes of individual insects was 16.3 s at 21.0C and 13.0 sat 27.8C. a. What is the apparent activation energy of the reaction that controls the flashing? b. What would be the average interval between flashes of an individual firefly at 30.0C? c. Compare the observed intervals and the one you calculated in part b to the rule of thumb that the Celsius temperature is 54 minus twice the interval between flashes.