Why does electrolysis of aqueous sodium chloride produce sodium hydroxide and chlorine gas?

The electrolysis of aqueous sodium chloride (brine) produces sodium hydroxide and chlorine gas through the passage of electric current through the solution, which causes chemical changes at the electrodes.12

When current is applied, the following reactions occur:

• At the Anode: Chloride ions ($C{l}^{-}$) are oxidized to form chlorine gas, which is then collected.2
• At the Cathode: Because reducing sodium ions ($N{a}^{+}$) in an aqueous environment is energetically unfavorable compared to reducing water, water molecules are reduced instead. This process produces hydrogen gas and leaves behind hydroxide ions ($O{H}^{-}$) in the solution.2

The combination of the remaining sodium ions and the newly formed hydroxide ions results in the production of sodium hydroxide, also known as caustic soda. In industrial settings, such as diaphragm or mercury cells, these products are carefully separated to prevent them from reacting with one another, ensuring the efficient production of chlorine and high-purity sodium hydroxide.2