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Positive standard cell potential correlates to K>1 because of the equation Delta G=-nFE. This shows that whenever E is positive, Delta G will be negative (moles are never negative and F is a positive constant). When Delta G is negative this means the reaction will be spontaneous and will favor products, or in other words K>1.
For a general reaction of the type aA + bB → cC + dD, the standard free-energy change and the equilibrium constant are related by the following equation: ΔG° = −RT lnK. Given the relationship between the standard free-energy change and the standard cell potential: ΔG° = −nFE°cell, we can write: −nFE°cell = −RT lnK. If you rearrange the equation to solve for E°cell, you get: E°cell = (RT/nF) lnK Thus E°cell is directly proportional to the logarithm of the equilibrium constant. This means that large equilibrium constants correspond to large positive values of E°cell and vice versa.
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