Organic Chemistry

134 CHAPTER 3 Alkenes• Thermodynamics and Kinetics

PROBLEM 20 SOLVED

At 30°C, the second-order rate constant for the reaction of methyl chloride and is

a. What is the rate of the reaction when and

b. If the concentration of methyl chloride is decreased to 0.01 M, what effect will this have

on the rateof the reaction?

c. If the concentration of methyl chloride is decreased to 0.01 M, what effect will this have

on the rate constantof the reaction?

SOLUTION TO 20a The rate of the reaction is given by

Substituting the given rate constant and reactant concentrations yields

PROBLEM 21

The rate constant for a reaction can be increased by _____ the stability of the reactant or by

_____ the stability of the transition state.

PROBLEM 22

From the Arrhenius equation, predict how

a. increasing the experimental activation energy will affect the rate constant of a reaction.

b. increasing the temperature will affect the rate constant of a reaction.

How are the rate constants for a reaction related to the equilibrium constant? At

equilibrium, the rate of the forward reaction must be equal to the rate of the reverse

reaction because the amounts of reactants and products are not changing:

Therefore,

From this equation, we can see that the equilibrium constant for a reaction can be de-

termined from the relative concentrations of the products and reactants at equilibrium

or from the relative rate constants for the forward and reverse reactions. The reaction

shown in Figure 3.3a has a large equilibrium constant because the products are much

more stable than the reactants. We could also say that it has a large equilibrium con-

stant because the rate constant of the forward reaction is much greater than the rate

constant of the reverse reaction.

Keq

k 1 [B]

= = k− 1 [A]

A B

k 1

k− 1

forward rate=reverse rate

k 1 [A]^ =k− 1 [B]^

=1.0* 10 -^7 Ms-^1

rate=1.0* 10 -^5 M-^1 s-^1 [0.10 M][0.10 M]

rate=k[methyl chloride] [HO-]

[CH 3 Cl]=0.10 M [HO-]=0.10 M?

1.0* 10 -^5 M-^1 s-^1.

HO-

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