Four Types of Reaction

Synthesis reactions

Synthesis reactions combine two or more reactants to create a single product. Typically, they require an input of energy, such as heat or light, to initiate the reaction. For example, the synthesis of water (2H₂ + O₂ → 2H₂O) illustrates this type of reaction.

Decomposition reactions

Decomposition reactions involve the breakdown of a single compound into simpler substances. Often exothermic, these reactions release energy in the form of heat. Examples include the thermal decomposition of calcium carbonate (CaCO₃ → CaO + CO₂) or the electrolysis of water (2H₂O → 2H₂ + O₂).

Single replacement reactions

In single replacement reactions, one element displaces another in a compound, forming a new compound and releasing the displaced element. The reactivity of elements, as determined by the activity series, is crucial. For instance, zinc replaces hydrogen in hydrochloric acid to form zinc chloride and hydrogen gas (Zn + 2HCl → ZnCl₂ + H₂).

Double replacement reactions

Double replacement reactions involve the exchange of ions between two compounds, leading to the formation of new compounds. These reactions often yield insoluble precipitates. For example, the reaction between silver nitrate and sodium chloride produces silver chloride as a white precipitate and sodium nitrate (AgNO₃ + NaCl → AgCl + NaNO₃).