Final answer:
To determine if a redox reaction is non-spontaneous, the standard cell potential is calculated. If it is negative, the reaction is non-spontaneous under standard conditions. The Nernst equation can also be used to predict spontaneity based on standard electrode potentials.
Step-by-step explanation:
To determine if a redox reaction will be non-spontaneous, you can calculate the standard cell potential (Eocell). The equilibrium constant (K) and the Gibbs free energy change (ΔG) are also important in this determination, as they are interrelated. If the standard cell potential is negative, the reaction is non-spontaneous under standard conditions.
Using the Nernst equation, the spontaneous direction of any redox reaction under nonstandard conditions can be predicted from the values of the standard electrode potentials. The equation shows that if the standard cell potential is positive, then the reaction is spontaneous, as implied by a negative ΔG. Conversely, if the standard cell potential is negative, then the reaction is non-spontaneous, indicated by a positive ΔG. Spontaneity can also be inferred by looking at a table of standard reduction potentials; if the half-reaction of the oxidizing agent is above the half-reaction of the reducing agent, the reaction is spontaneous under standard conditions.
Remember that spontaneity doesn't necessarily mean the reaction will proceed quickly; this is where kinetics comes into play. The rate constant and activation energy provide information on the rate of the reaction but not its spontaneity. Thus, relying on the cell potential values and their relation to Gibbs free energy change is the most direct method to assess the spontaneity of redox reactions.