Calculating the equilibrium constant

What is the relationship between the Nernst equation and the equilibrium constant?

When an electrochemical cell discharges, its electrolyte’s concentration changes. The concentrations of the reaction species stop changing when the overall reaction reaches equilibrium. When this happens, no electrons flow in the circuit and E = 0. The Nernst equation becomes,


where K is the equilibrium constant or the reaction quotient at equilibrium. We can therefore determine K:


For example, the equilibrium constant for the reaction

Cu(s)+2Ag^+(aq)\rightleftharpoons Cu^{2+}(aq)+2Ag(s)\; \; \; \; \; \; E^o=+0.46\; V


K=e^\frac{2\times 96485\times 0.46}{8.31\times 298}=3.69\times 10^{15}


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