Page 174 - Modern physical chemistry

166 Relationships among Reactants

7.6 What can cause the calorimetric entropy to be in error?
7.7 Estimate the entropy excess for (a) CO, (b) H2 0.
7.8 How does one obtain (a) the standard Gibbs energy change, (b) the standard Helmholtz
energy change, in a reaction from calorimetric data?
7.9 How is the chemical potential related to the activity of a constituent in a phase?
7.10 Define the Gibbs energy of reaction and the Helmholtz energy of reaction.
7.11 Distinguish between the pressure reaction quotient, the concentration reaction quotient,
and the activity reaction quotient.
7.12 Distinguish between equilibrium constants K, Kp, and Kc.
7.13 How are these equilibrium constants related to changes in thermodynamic properties?
7.14 How does one employ an equilibrium constant in determining the equilibrium state for a
gaseous system?
7.15 How are heterogeneous gas equilibria treated?
7.16 Explain how equilibrium constants vary with (a) temperature, (b) pressure.
7.17 Define and describe an activity coefficient (a) for partial pressure, (b) for concentration.

Problems

7.1 When 60.0 ml 0.500 M acetic acid was mixed with 60.0 ml 0.500 M sodium hydroxide, the tem-
perature rose from 25.00 0 to 27.55 0 C. If the energy capacity of the 0.250 M sodium acetate
formed was 4.029 J Kl g-l , its density 1.034 g ml- l , and the effective energy capacity of the empty
calorimeter 150.6 J Kl , what is !:J{ for the corresponding neutralization of 1 mole acetic acid?
7.2 When 1 mole liquid n-pentane, CJ:I12, is oxidized completely to gaseous CO2 and liquid H2 0
at 25 0 C, !:J{ is -3509.5 kJ. Calculate tlE for the reaction.
7.3 From the reaction heats

co (g) +! O2 (g) ~ CO2 (g), tJf&S.15 = -282.96 kJ,
2
1
H2 (g)+-02 (g)~ H20 (g), tJf&S.15 = -241.84 kJ,
2
calculate Mf! 2f118.l5 for
CO2 (g) + H2 (g) ~ CO (g) + H20 (g).
7.4 Calculate the entropy of solid NH 40H at 15.0 K, where its energy capacity Cp is
1. 753 J Kl mot l •
7.5 Calculate the calorimetric entropy of titanium at 298.15 K from the data in table 7.D.
TABLE7.D

T,K Cpt J KI mot l T,K Cpt J KI mot l
0 0.000 150 19.598
15 0.167 175 21.100
25 0.657 200 22.263
50 4.753 225 23.175
75 10.050 250 23.903
100 14.368 275 24.535
125 17.385 298.15 25.004

7.6 Show that in a solid solution of AgCI in AgBr, the Nl chloride ions and the N2 bromide ions
can be arranged in N!/(NI !N2!) different ways. Then calculate the entropy at 0 K of a homo-
geneous phase containing 10.0 g AgCI and 50.0 g AgBr.