At room temperature (20°C) milk sours in about 64 hours. In a refrigerator (3°C) milk can be stored for approximately three times as long.Estimate the activation energy of the reaction that causes the souring of milk.

11.44 A possible reaction for the degradation of the pesticide DDT to a less harmful compound was simulated in the laboratory. The reaction was found to be first order, with k = 4.0 X 10_H s"' at 25°C. What is the half-life for the degradation of DDT in this experiment, in years?

A popular chemical demonstration is the magic genie procedure, in which hydrogen peroxide decomposes to water and oxygen gas with the aid of a catalyst. The activation energy of this (uncatalyzed) reaction is 70.0 kJ/mol. When the catalyst is added, the activation energy (at 20.C) is 42.0 kJ/mol. Theoretically, to what temperature (C) would one have to heat the hydrogen peroxide solution so that the rate of the uncatalyzed reaction is equal to the rate of the catalyzed reaction at 20.C? Assume the frequency factor A is constant, and assume the initial concentrations are the same.

Consider the hypothetical reaction A2(g) + B2(g) 2AB(g), where the rate law is: [A2]t=k[A2][B2] The value of the rate constant at 302C is 2.45 104 L/mol s, and at 508C the rate constant is 0.891 L/mol s. What is the activation energy for this reaction? What is the value of the rate constant for this reaction at 375C?

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?

(Section 11-5) A rule of thumb is that for a typical reaction, if concentrations are unchanged, a 10-K rise in temperature increases the reaction rate by two to four times. Use an average increase of three times to answer the questions below. (a) What is the approximate activation energy of a typical chemical reaction at 298 K? (b) If a catalyst increases a chemical reactions rate by providing a mechanism that has a lower activation energy, then what change do you expect a 10-K increase in temperature to make in the rate of a reaction whose uncatalyzed activation energy of 75 kJ/mol has been lowered to one half this value (at 298 K) by addition of a catalyst?

Consider a reaction in which E a=129 kJ and H=29 kJ. In the presence of a catalyst, the activation energy is 48% of the uncatalyzed reaction. Follow the directions in Question 71 in drawing an energy diagram.