What is the gas evolution in electrolysis and why does it occur?

Gas evolution in electrolysis refers to the production of gases at the electrodes due to the breakdown of compounds.

During electrolysis, an electric current is passed through an electrolyte (a substance that conducts electricity). This causes the electrolyte to break down into its constituent elements, a process known as electrolytic decomposition. The elements produced can be in the form of gases, which are then evolved at the electrodes.

The type of gas produced depends on the electrolyte used and the type of electrodes. For instance, if the electrolyte is water, hydrogen gas will be evolved at the cathode (negative electrode) and oxygen gas at the anode (positive electrode). This is because water is made up of hydrogen and oxygen, and these elements are released when it is broken down.

Gas evolution occurs due to the movement of ions in the electrolyte. When the electric current is passed through the electrolyte, the positively charged ions move towards the cathode and the negatively charged ions move towards the anode. At the electrodes, these ions gain or lose electrons (a process known as reduction or oxidation respectively) and are transformed into neutral atoms or molecules. If these atoms or molecules are in the gaseous state, they will be evolved as gas at the electrodes.

In summary, gas evolution in electrolysis is a result of the electrolytic decomposition of the electrolyte, driven by the electric current. The type of gas evolved depends on the electrolyte and the electrodes used. This process is fundamental to many industrial processes, such as the production of chlorine gas from brine or the production of hydrogen gas for use in fuel cells.