Question

Electrolysis of water is an example of a ____________ (decomposition/combination) reaction.

Answer 1

Decomposition reaction

• In a decomposition reaction, complex compound is broken down into two or more simpler compounds.
• A source of energy, such as heat, light, or electricity, is required for most of the decomposition reactions.
• Based on the source of energy, decomposition reactions are divided into 3 types-

1. Electric decomposition / Electrolysis
2. Photo decomposition
3. Thermal decomposition

Electric decomposition / Electrolysis

• When decomposition reactions takes place in presence of electricity, it is called electrical decomposition reaction or Electrolysis.
• For example, Electrolysis of water
• $\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\stackrel{\mathrm{Electricity}}{\to }\underset{\mathrm{Hydrogen}}{2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$

Photo decomposition

• When decomposition reactions takes place in presence of sunlight, it is called photo decomposition reaction.
• For example, $\underset{\mathrm{Silver}\mathrm{Chloride}}{2\mathrm{AgCl}\left(\mathrm{s}\right)}\stackrel{\mathrm{Sunlight}}{\to }\underset{\mathrm{Silver}}{2\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Chlorine}}{{\mathrm{Cl}}_2\left(\mathrm{g}\right)}$

Thermal decomposition

• When decomposition reactions takes place in presence of heat, it is called thermal decomposition reaction.
• For example, $\underset{\mathrm{Ferrous}\mathrm{Sulphate}}{{\mathrm{FeSO}}_4\left(\mathrm{s}\right)}\stackrel{\mathrm{Heat}}{\to }\underset{\mathrm{Ferric}\mathrm{oxide}}{{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Sulphur}\mathrm{trioxide}}{{\mathrm{SO}}_3\left(\mathrm{g}\right)}$

Hence, Electrolysis of water is an example of a decomposition (decomposition/combination) reaction.