Chemistry

At equilibrium, the driving force for the redox reaction vanishes—no net electron transfer occurs. This means the cell potential $E_{cell}$ must equal zero. The key insight is that $E_{cell}$ and the reaction quotient $Q$ are linked through the Nernst equation: when $E_{cell} = 0$, we can solve for the condition on $Q$, which turns out to equal the equilibrium constant $K$. So at equilibrium, $E_{cell} = 0$ and $Q = K$.

At equilibrium, the driving force for the redox reaction vanishes—no net electron transfer occurs. This means the cell potential $E_{cell}$ must equal zero. The key insight is that $E_{cell}$ and the reaction quotient $Q$ are linked through the Nernst equation: when $E_{cell} = 0$, we can solve for the condition on $Q$, which turns out to equal the equilibrium constant $K$. So at equilibrium, $E_{cell} = 0$ and $Q = K$.