Consider an electrochemical cell : A(s) | A n+ (aq, 2 M) || B 2n+ (aq, 1 M) | B(s). The value of Δ H° for the cell reaction is twice that of Δ G° at 300 K. If the emf of the cell is zero, the Δ S°(in J K –1 mol –1 ) of the cell reaction per mole of B formed at 300 K is____. (Given : ln
Text Solution
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–11.62 JK –1 mol –1
Sol. A(s)|A n+ (aq, 2M) || B 2n+ (aq, 1M) | B(s)
Reactions
Anode (A ⎯→ A n+ + ne) × 2
Cathode B 2n+ + 2ne ⎯→ B
Overall reaction :
2A(s) + B 2n+ ⎯→ 2A n+ + B.
E = Eº – 
O = Eº – 
Eº = 
Now Δ Gº = –2nFEº = 
= –RT λ n4.
Δ Gº = Δ Hº –T Δ Sº = 2 Δ Gº = –T Δ Sº
T Δ Sº = Δ Gº
Δ Sº = 
= 
= –R λ n4
= –8.3 × 2 × 0.7 = –11.62 JK –1 mol –1
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