Combination reactions occur when substances combine to form a compound, while decomposition reactions involve the breakdown of a compound into new substances.
Combination and decomposition reactions can be identified based on their characteristics.
Combination reactions occur when two or more substances combine to form a single compound. These reactions often release energy and can be represented by the general equation: A + B → AB. For example, the reaction of hydrogen gas (H2) with oxygen gas (O2) to form water (H2O) is a combination reaction: 2H2 + O2 → 2H2O.
Decomposition reactions, on the other hand, occur when a single compound breaks down to form two or more new substances. These reactions are often initiated by heat or the presence of a catalyst. An example of a decomposition reaction is the breakdown of hydrogen peroxide (H2O2) into water (H2O) and oxygen gas (O2): 2H2O2 → 2H2O + O2.