How do you determine the electrical potential of a half reaction

Question

GPT 3.5 · Answer

The electrical potential of a half reaction can be determined using a standard reduction potential table, which lists the standard reduction potentials (E°) of various half reactions.

To determine the electrical potential of a half reaction, follow these steps:

1. Identify the half reaction: Determine whether the half reaction is an oxidation (losing electrons) or reduction (gaining electrons) half reaction. This is important because the standard reduction potentials are given for reduction half reactions. If the given half reaction is an oxidation, you need to reverse the reaction to obtain the corresponding reduction half reaction.

2. Locate the half reaction in the standard reduction potential table: Look for the half reaction and find its corresponding standard reduction potential (E°) in the table. The standard reduction potential is typically given in volts (V) or millivolts (mV).

3. Note the sign of the standard reduction potential: The sign of the standard reduction potential indicates whether the reaction is spontaneous or non-spontaneous. A positive standard reduction potential (E° > 0) indicates that the reaction is spontaneous, while a negative standard reduction potential (E° < 0) indicates that the reaction is non-spontaneous.

4. Calculate the electrical potential of the half reaction: The electrical potential (E) of the half reaction can be calculated using the Nernst equation: E = E° - (0.0592/n) * log(Q), where E° is the standard reduction potential, n is the number of electrons transferred in the reaction, and Q is the reaction quotient. The reaction quotient (Q) is the ratio of the concentrations of the reaction products to the concentrations of the reactants, each raised to the power of their stoichiometric coefficients. If the reaction is at standard conditions (all concentrations are 1 M), then the log(Q) term becomes zero, and the equation simplifies to E = E°.

It's important to note that the electrical potentials calculated using the Nernst equation are not the same as the standard reduction potentials (E°) listed in the table. The Nernst equation takes into account the effect of concentration and temperature on the electrical potential.