Final answer:
To determine if a redox reaction is spontaneous, use the equation Ecell = Ecathode - Eanode, where a positive Ecell suggests spontaneity. Standard electrode potentials help predict spontaneity, but the Nernst equation provides a refined prediction by including reactant and product concentrations.
Step-by-step explanation:
To determine if a redox reaction will be spontaneous, you can use the equation Ecell = Ecathode - Eanode. A positive Ecell value indicates that a reaction is spontaneous. The strength of the oxidant and the reductant can be found in a standard electrode potential table, where a more positive E° indicates a stronger oxidizing agent. In a spontaneous redox reaction, the oxidant, which is the substance being reduced, typically has a more positive standard electrode potential than the reductant, or the substance being oxidized. Consequently, the substance with the higher electrode potential functions as the cathode, and the one with the lower potential acts as the anode.
The Nernst equation can refine this prediction by accounting for non-standard conditions such as concentration changes. For instance, altering the concentration of reactants can shift the spontaneity of the reaction. This balance can be calculated using the Nernst equation, which includes the concentrations of the reactants and products to find the actual cell potential under given conditions, thus predicting the spontaneity more accurately.
In summary, a spontaneous redox reaction is expected when the Ecell calculated from standard electrode potentials is positive (E° cathode > E° anode). However, reaction conditions, including reactant concentrations, which are accounted for by the Nernst equation, can also affect spontaneity.