Chapter 15, Problem 96E

Consider the reaction in which HCI adds across the double bond of ethene:

$\text{HCL}+{\text{H}}_{\text{2}}\text{C}={\text{CH}}_{\text{2}}\to {\text{H}}_{\text{3}}\text{C}-{\text{CH}}_{\text{2}}\text{Cl}$

The following mechanism, with the accompanying energy diagram has been suggested for this reaction:

Step 1 $\text{HCL}+{\text{H}}_{\text{2}}\text{C}={\text{CH}}_{\text{2}}\to {\text{H}}_{\text{3}}{\text{C=CH}}_{\text{2}}{}^{\text{+}}+{\text{Cl}}^{-}$

Step 2 ${\text{H}}_{\text{3}}\text{C}={\text{CH}}_{\text{2}}{}^{+}+{\text{Cl}}^{-}\to {\text{H}}_{\text{3}}\text{C}-{\text{CH}}_{\text{2}}\text{Cl}$

a. Based on the energy diagram, determine which step is rate limiting.
b. What is the expected order of the reaction based on the proposed mechanism?
c. Is the overall reaction exothermic or endothermic?