This decomposition reaction lab experiment involves the breakdown of a compound into two or simpler substances. Most decomposition reactions require energy input from heat, light, or electricity. Binary mixtures are made up of only two elements. When a binary compound decomposes into its constituents, this is the most basic type of decomposition reaction. When heated, mercury (II) oxide, a red solid, decays to produce mercury and oxygen gas. Even if one or more products are still compounds, a reaction is considered a decomposition reaction. In this decomposition reaction lab experiment, a metal carbonate decomposes into metal oxide and carbon dioxide gas.