Thermodynamics and Chemistry

CHAPTER 11 REACTIONS AND OTHER CHEMICAL PROCESSES

PROBLEMS 359

Problems

An underlined problem number or problem-part letter indicates that the numerical answer appears

in AppendixI.

11.1 Use values ofÅfHandÅfGin AppendixHto evaluate the standard molar reaction enthalpy
and the thermodynamic equilibrium constant at298:15K for the oxidation of nitrogen to form
aqueous nitric acid:
1
2 N^2 .g/C

5

4 O^2 .g/C

1

2 H^2 O.l/!H

C.aq/CNO 3 .aq/

11.2 In 1982, the International Union of Pure and Applied Chemistry recommended that the value
of the standard pressurepbe changed from 1 atm to 1 bar. This change affects the values of
some standard molar quantities of a substance calculated from experimental data.
(a)Find the changes inHm,Sm, andGmfor a gaseous substance when the standard pressure
is changed isothermally from1:01325bar ( 1 atm) to exactly 1 bar. (Such a small pressure
change has an entirely negligible effect on these quantities for a substance in a condensed
phase.)
(b)What are the values of the corrections that need to be made to the standard molar enthalpy
of formation, the standard molar entropy of formation, and the standard molar Gibbs
energy of formation of N 2 O 4 (g) at298:15K when the standard pressure is changed from
1:01325bar to 1 bar?

11.3 From data for mercury listed in AppendixH, calculate the saturation vapor pressure of liquid
mercury at both298:15K and273:15K. You may need to make some reasonable approxima-
tions.

11.4 Given the following experimental values atTD298:15K,pD 1 bar:

HC(aq)COH(aq)!H 2 O(l) ÅrHD55:82kJ mol^1

Na(s)CH 2 O(l)!NaC(aq/COH(aq)C^12 H 2 (g) ÅrHD184:52kJ mol^1

NaOH(s)!NaOH(aq) ÅsolH^1 D44:75kJ mol^1

NaOH in 5 H 2 O!NaOH in 1 H 2 O ÅHm(dil)D4:93kJ mol^1

NaOH(s) ÅfHD425:61kJ mol^1

Using only these values, calculate:

(a)ÅfHfor NaC(aq), NaOH(aq), and OH(aq);

(b)ÅfHfor NaOH in 5 H 2 O;

(c)ÅHm(sol) for the dissolution of 1 mol NaOH(s) in 5 mol H 2 O.