Physical Chemistry Third Edition

362 8 The Thermodynamics of Electrochemical Systems

HCI

solution

Hg(I)

Hg 2 Cl 2 (s)

Pt Pt

H 2

Figure 8.3 An Electrochemical Cell with a Hydrogen Electrode and a Calomel

Electrode.

HCI

solution

Hg(I)

Hg 2 Cl 2 (s)

Pt

AgCl(s)

Pt

Ag

Figure 8.4 An Electrochemical Cell with a Silver–Silver Chloride Anode and a Calo-

mel Cathode.

Now consider the cell shown in Figure 8.4. This cell contains a silver–silver chloride

electrode on the left, a calomel electrode on the right, and an aqueous solution of HCl.

We construct a double cell as depicted in Figure 8.5. This double cell consists of two

complete cells, one of which is the cell of Figure 8.3. The other cell is obtained by

interchanging the right and left half-cells of Figure 8.2. It has the cell reaction equation

2HCl+2Ag(s)+ 2 e−(R)−→H 2 (g)+2AgCl(s)+ 2 e−(L) (8.3-2)