20.71.For the following two reactions
H Cl 2 →HCl Cl
H Br 2 →HBr Brthe first reaction has a lower value of Athan the second reac-
tion. What can one say about the relative properties of the in-
termediates HCl 2 and HBr 2 , just from the relative values of A?
20.72.For the reaction
NaI Cl →NaCl Ipropose a structure for the transition state and list what data are
needed to determine a value of kusing transition-state theory.
20.73.Explain how (or if ) equation 20.84 is consistent with
the general statements of the laws of thermodynamics that
reactions tend toward lower energy and higher entropy.
20.74.If all other factors are the same, a change in S* from
1 J/(molK) to 1 J/(molK) leads to what percentage change
in the rate constant k?
20.75.Consider a reaction that has two parallel pathways
(both first-order) to products. Pathway 1, leading to product
B, has a rate constant of 1.34 10 ^5 s^1. Product C–
producing pathway 2 has a rate constant of 6.55 10 ^4 s^1.
Plot the concentrations of A, B, and C versus time, and deter-
mine the time necessary to produce the maximum amount of
the kinetically favored product.
20.76.Consider a set of first-order consecutive reactions
A →B →C. The rate constants are 8.4 10 ^4 s^1 and
3.02 10 ^5 s^1 , respectively. Plot the concentrations of A, B,
and C versus time, and determine the time necessary to pro-
duce the maximum amount of the intermediate product B.730 Exercises for Chapter 20
Symbolic Math Exercises