A button cell used in watches functions as following \mathrm{Zn}(s)+\mathrm{Ag}_2 \mathrm{O}(s) & +\mathrm{H}_2 \mathrm{O}(l) \rightleftharpoons 2 \mathrm{Ag}(s) + \mathrm{Zn}^{2+}(\alpha q)+2 \mathrm

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A button cell used in watches functions as following \mathrm{Zn}(s)+\mathrm{Ag}_2 \mathrm{O}(s) & +\mathrm{H}_2 \mathrm{O}(l) \rightleftharpoons 2 \mathrm{Ag}(s) + \mathrm{Zn}^{2+}(\alpha q)+2 \mathrm{OH}^{-}(\alpha q) If half cell potentials are Zn 2 + ( a q ) + 2 e − Ag 2 ​ O ( s ) + H 2 ​ O ( l ) ​ → Zn ( s ) ; E ∘ = − 0.76 V + 2 e − → 2 Ag ( s ) + 2 OH − ( a q ) , E ∘ = 0.34 V ​ The cell potential will beNEET 2013 (All India)

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Anode is always the site of oxidation thus anode half cell is Zn 2 + ( aq ) + 2 e − ⟶ Zn ( s ) ; E ∘ = − 0.76 V Cathode half cell is ​ Ag 2 ​ O ( s ) + H 2 ​ O ( l ) + 2 e − ⟶ 2 Ag ( s ) + 2 OH E − ( a q ) ; E ∘ = 0.34 V = E cathode ∘ ​ − E anode ∘ ​ = 0.34 − ( − 0.76 ) = + 1.10 V ​

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