(a) What conditions must be met for a reduction potential to be a standard reduction potential? (b) What is the standard reduction potential of a standard hydrogen electrode? (c) Why is it impossible to measure the standard reduction potential of a single half-reaction?

To be considered a standard reduction potential, a reduction potential must meet the following conditions: 1. Temperature: The measurement must be taken at a temperature of 298 K (25 degrees Celsius). 2. Pressure: The pressure must be set at 1 atmosphere (atm) or 101.325 kPa. 3. Concentration: The concentration of each ion in the reaction must be 1 M (1 mol L^-1). By keeping these conditions constant, it is possible to compare the reduction potentials of various half-reactions.

The standard hydrogen electrode (SHE) is a common reference electrode used in electrochemistry. It consists of a platinum wire coated with a thin layer of platinum black, and it is immersed in an acidic solution (pH = 0) containing hydrogen ions (H+) with a concentration of 1 M. Hydrogen gas (H2) is continuously bubbled through the solution at a pressure of 1 atm. By definition, the SHE is assigned a standard reduction potential of 0 Volts (V) under standard conditions (298 K, 1 atm, and 1 M concentration). This value serves as a reference point for measuring and comparing the standard reduction potentials of other electrodes.

In electrochemistry, a half-reaction represents either the reduction or oxidation process in an overall redox reaction. The standard reduction potential of a half-reaction is the potential difference between the half-reaction and the SHE under standard conditions. However, it is impossible to measure the standard reduction potential of a single half-reaction because there is no flow of electrons between the half-reaction and SHE when they are isolated from each other. The flow of electrons occurs only when both half-reactions are connected to form a complete redox reaction within an electrochemical cell. To measure the standard reduction potential of a half-reaction, the half-reaction must be paired with another half-reaction to form a complete redox reaction. By connecting the two half-reactions to form an electrochemical cell, a potential difference can be measured between them. This potential difference represents the sum of the standard reduction potentials of the two half-reactions. Since the standard reduction potential of the SHE is defined as 0 V, comparing the measured potential difference between the unknown half-reaction and the SHE directly gives the standard reduction potential of the unknown half-reaction. Thus, it is impossible to measure the standard reduction potential of a single half-reaction because an electrochemical cell requires two half-reactions (connected in a complete redox reaction) for a potential difference to exist and be measured.