Thermodynamics and Chemistry

CHAPTER 14 GALVANIC CELLS

PROBLEMS 468

(b)Use the data to evaluate the standard molar enthalpy of formation and the standard mo-

lar Gibbs energy of formation of crystalline silver chloride at298:15K. (Note that this

calculation provides values of quantities also calculated in Prob. 14. 3 using independent

data.)

14.5 Use data in Sec.14.3.3to evaluate the solubility product of silver chloride at298:15K.

14.6 The equilibrium cell potential of the galvanic cell

Pt H 2 (g,fD 1 bar) HCl(aq,0:500mol kg^1 ) Cl 2 (g,fD 1 bar) Pt

is found to beEcell, eqD1:410V at298:15K. The standard cell potential isEcell, eq D1:360V.

(a)Write the cell reaction and calculate its thermodynamic equilibrium constant at298:15K.

(b)Use the cell measurement to calculate the mean ionic activity coefficient of aqueous HCl

at298:15K and a molality of0:500mol kg^1.

14.7 Consider the following galvanic cell, which combines a hydrogen electrode and a calomel
electrode:
Pt H 2 .g/ HCl.aq/ Hg 2 Cl 2 .s/ Hg.l/ Pt
(a)Write the cell reaction.
(b)At298:15K, the standard cell potential of this cell isEcell, eqD0:2680V. Using the value
ofÅfGfor the aqueous chloride ion in AppendixH, calculate the standard molar Gibbs
energy of formation of crystalline mercury(I) chloride (calomel) at298:15K.
(c)Calculate the solubility product of mercury(I) chloride at298:15K. The dissolution equi-
librium is Hg 2 Cl 2 .s/ ï Hg 22 C.aq/C2 Cl.aq/. Take values for the standard molar
Gibbs energies of formation of the aqueous ions from AppendixH.

Table 14.1 Equilibrium cell poten-

tial as a function of HBr molalitymB.

mB/ (mol kg^1 ) Ecell, eq/ V

0.0004042 0.47381

0.0008444 0.43636

0.0008680 0.43499

0.0013554 0.41243

0.001464 0.40864

0.001850 0.39667

0.002396 0.38383

0.003719 0.36173

14.8 Table14.1lists equilibrium cell potentials obtained with the following cell at298:15K:^6

Pt H 2 (g,1:01bar) HBr(aq,mB) AgBr(s) Ag

Use these data to evaluate the standard electrode potential of the silver-silver bromide electrode

at this temperature to the nearest millivolt. (Since the electrolyte solutions are quite dilute, you

may ignore the termBapmBin Eq.14.5.2.)

(^6) Ref. [ 91 ].