AgBr = Ag+ + Br- 以上两个反应相加： AgBr + e- = Ag + Br-
K?4.9?10?13??rGm??RTlnK?70225.22J/mol
?rGm?0.0713V ?zF?rGm??6878.3J/mol???即?(Ag|AgBr)?0.0713V，故E??0.0713V
（3）由Nernst方程，E?E?0.01p/pRTln????0.51 F(??b/b)213. 试说明对消法测定电池电动势的原理。
【略】请参见教材第60页。
14. At 298 K the standard formation Gibbs function for C2H5OH(l) and C2H4(g) are -174.77 and 68.18 kJ/mol respectively, the saturated vapor pressure of ethyl-alcohol is 7599 Pa, and the values of standard electrode potential for OH- | H2 | Pt and Pt | O2 | OH- are -0.8277 V and 0.401 V
H? respectively. Find the equilibrium constant for the following reaction: C2H4(g) + H2O(l) ??+C2H5OH(g)
Solution: For cell reaction
H2 +
design
Pt | H2 | OH- | O2 | Pt
standard e.m.fE?0.401?0.8277?1.229V
1O2 = H2O(l) 2?rGm??zFE??237139J/mol
Thus, ?fGm(H2O)??237.14kJ/mol
H? C2H5OH(l) C2H4(g) + H2O(l) ??+
(1) (2) (3)
C2H5OH(l) = C2H5OH(g)
+
H? C2H5OH(g) C2H4(g) + H2O(l) ???rGm(1)??174.77?68.18?237.14??5.81kJ/mol ???G(1)?K(1)?exp?rm??10.434
RT??K(2)?1?0.075 p/pSince (1) + (2) = (3), we have the equilibrium constant
K(3)?K(1)?K(2)?0.783
16