Chemical Reactions

There are mainly four types of chemical reactions:

• Composition Reactions
• Decomposition Reactions
• Single Displacement Reactions
• Double Displacement Reactions

Composition Reactions

When two or more compounds/elements combine to “compose” a single compound, the reaction is called a composition reaction/combination reaction.

Examples:

• \(\ce{N2 + 3H2 \rightarrow 2NH3}\) (2 elements combining)
• \(\ce{CaO + CO2 \rightarrow CaCO3}\) (2 compounds combining)
• \(\ce{CO + \frac{1}{2}O2 \rightarrow CO2}\) (an element and a compounds combining)

Decomposition Reactions

When a single compound decomposes to form more than one compounds/elements, the reaction is called decomposition reaction. In other words, these reactions are opposites of composition reactions. It can be of several types, like thermal decomposition, electrolytical decomposition, photochemical decomposition, etc.

Examples:

• \(\ce{Pb(NO3)2 \xrightarrow{\text{heat}} PbO + 2NO2 + \frac{1}{2}O2}\) (thermal decomposition)
• \(\ce{2H2O \xrightarrow{\text{electricity}} 2H2 + O2}\) (electrolytical decomposition)
• \(\ce{AgCl \xrightarrow{\text{hv}} Ag + \frac{1}{2}Cl2}\) (photochemical decomposition)

We shall cover the other two types on the next page.

Written by Vasu Vijay