Standard Electrode Potential

The standard electrode potential, written $E^0$, is the electrode potential measured under one fixed, agreed set of conditions: every species taking part in the electrode reaction at unit concentration, and the temperature at 298 K. To make $E^0$ values comparable across different redox couples, one reference point is fixed by international convention: the standard hydrogen electrode is assigned $E^0 = 0.00$ V exactly, and every other couple's $E^0$ is measured relative to it. By convention, the electrode reaction used when tabulating a couple's $E^0$ is always written as a REDUCTION (oxidised form + n e⁻ → reduced form), so the value and sign of $E^0$ directly measure how strongly that couple's oxidised species tends to grab electrons and stay in its reduced form, compared with the H⁺/H2 reference couple. A large POSITIVE $E^0$ therefore marks a strong oxidising agent -- fluorine, at $E^0 = +2.87$ V, has by far the greatest tendency of any species in Table 6.1 to gain an electron, making it the strongest oxidising agent listed. A large NEGATIVE $E^0$ marks a strong reducing agent, meaning that redox couple is a stronger reducing agent than H⁺/H2 itself -- the alkali metals sit at the most negative end of the table (lithium at $E^0 = -3.05$ V, potassium at $-2.93$ V, sodium at $-2.71$ V), reflecting their group-wide tendency to give away their single outer electron easily and form cations, which is exactly what makes a metal a strong reducing agent. Given the $E^0$ values of two redox couples, it is possible to predict whether a reaction between them will happen spontaneously (Problem 6.9): write a reduction half reaction for one species using its tabulated $E^0$, write an oxidation half reaction for the other species by reve …