Make sure you thoroughly understand the following essential ideas. It is especially important that you know the precise meanings of all the highlighted terms in the context of this topic.

• The Nernst equation relates the effective concentrations (activities) of the components of a cell reaction to the standard cell potential. For a simple reduction of the form Mn+ + ne– → M, it tells us that a half-cell potential will change by 59/n mV per 10-fold change in the activity of the ion.
• Ionic concentrations can usually be used in place of activities when the total concentration of ions in the solution does not exceed about about 0.001M.
• In those reactions in which H+ or OH–ions take part, the cell potential will also depend on the pH. Plots of E vs.pH showing the stability regions of related species are very useful means of summarizing the redox chemistry of an element.