CH302H - Principles of Chemistry II: Honors
Spring 2016, Unique 49420

Homework, Week 14

Homework, week 14
Answer key

1.  What are the units of the pre-exponential factor A in the Arrhenius equation?

2.  Initial rates for the following reaction have been obtained at a variety of temperatures:

                        OH(g) + ClCH2CH2Cl(g) --> H2O(g) + ClCHCH2Cl(g)

                        T (K)            k (108 L mol-1 s-1)

                        292            1.24

                        296            1.32

                        321            1.81

                        333            2.08

                        343            2.29

                        363            2.75

            a)  Determine the values of Ea and A for this reaction.

            b)  At what temperature will the rate of the reaction be twice the rate measured at 363 K?

3.  Cyclohexane converts between two stable structures, the so-called “chair” and “boat” conformations.  The enthalpy and entropy of the formation of the activated complex are known to be 31.9 KJ mol-1 and 16.7 J K-1 mol-1, respectively. 

            a)  Determine the Gibbs energy of activation and the rate constant for this conversion. 

            b)  Based on the value of the enthalpy and entropy of the activated complex, hypothesize what the structure of the transition state might be.

4.  H2(g) and I2(g) react in one elementary step to form HI. 

            a) Write out this reaction mechanism.

            b) The entropy of the transition state is known to be > 0.  Use all of this information to propose a structure of the transition state.

5.  (Download the pdf to see the figure.)  The reaction H(g) + H2(g) --> H2(g) + H(g) has been studied extensively to understand basic mechanisms of gas phase reaction dynamics.  A contour plot of the potential energy surface of the collinear collision of H and H2 is shown below, where r12 is the bond length of the reactant H2 and r23 is the bond length of the product H2. 

            a) Label the transition state.

            b) Draw a dashed line that indicates the lowest energy path of the reaction. 

            c) What is the distance between H and each hydrogen of the H2 atom in the transition state?  A drawing of the transition state would probably help you answer this problem succinctly.