(b) Write the half-reaction that occurs at a hydrogen electrode in acidic aqueous solution when it serves as the anode of a voltaic cell.

A half-reaction represents either the oxidation or reduction process occurring in an electrochemical cell. In the context of a voltaic cell, the anode undergoes oxidation, where electrons are released. Understanding half-reactions is crucial for balancing redox reactions and determining the flow of electrons in electrochemical systems.

A voltaic cell, also known as a galvanic cell, is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two electrodes (anode and cathode) immersed in electrolyte solutions. The anode is where oxidation occurs, while reduction takes place at the cathode, generating a flow of electrons that can be harnessed for electrical power.

An acidic aqueous solution contains a higher concentration of hydrogen ions (H+) than hydroxide ions (OH-), typically with a pH less than 7. In the context of the hydrogen electrode, the presence of H+ ions facilitates the reduction of protons to hydrogen gas at the cathode or the oxidation of hydrogen gas to protons at the anode. This environment is essential for understanding the reactions that occur at the hydrogen electrode in electrochemical cells.