DAT Bootcamp General Chemistry Practice Test

The main idea is that the cell potential depends on the reaction quotient through the Nernst equation. At 25°C, Ecell = E°cell − (0.0592/n) log Q, where Q is the activities of products over reactants for the overall cell reaction.

If the system shifts toward the right (toward products), the concentrations adjust in a way that can lower Q for a common galvanic cell such as Cu2+ + Zn → Cu + Zn2+. In this reaction, Q = [Zn2+]/[Cu2+]. Increasing the oxidizing agent (Cu2+) while not increasing Zn2+ pushes the equilibrium to the right and reduces Q. A smaller Q makes log Q less positive (or more negative), so the term subtracted becomes smaller in magnitude, and Ecell increases. Thus, moving toward the products can raise the cell potential.

Remember, if shifting toward the right were accompanied by increasing product concentrations in a way that raises Q, Ecell would decrease. The key is how Q changes with the shift toward products.