In chemistry, a **reactant** is a substance that undergoes a chemical change or reaction when it interacts with another substance, called a reagent or another reactant, to form a product. Reactants are the starting materials in a chemical process, and their properties and quantities determine the outcome of the reaction. They are typically written on the left side of a chemical equation. The rate at which a reaction occurs is often influenced by the concentration of reactants, temperature, and presence of catalysts. Effective reactions occur when the reactants have sufficient energy, appropriate orientation and come in contact.
Reactant meaning with examples
- In the combustion of methane, **methane** (CH₄) and **oxygen** (O₂) are the reactants. They react when ignited, forming carbon dioxide and water. The amount of oxygen available determines how complete the reaction is. An excess of reactants will yield more product unless another factor limits the reaction.
- During photosynthesis, **carbon dioxide** (CO₂) and **water** (H₂O) are the primary reactants. They are converted into glucose (sugar) and oxygen (O₂) with energy from sunlight. This is a critical reaction for plant life. The reaction uses the absorption of light energy.
- In the neutralization of hydrochloric acid (HCl) with sodium hydroxide (NaOH), **HCl** and **NaOH** are the reactants. They react to produce water (H₂O) and sodium chloride (NaCl) which is table salt. The reaction is determined by the reaction's concentration and molarity.
- When iron (Fe) rusts, **iron** and **oxygen** (along with water, often) are the key reactants. The product is iron oxide (rust). The reaction is slow under normal conditions but can be accelerated with high temperatures and humidity. The presence of salt increases the process speed.
- In the Haber-Bosch process for synthesizing ammonia (NH₃), **nitrogen** (N₂) and **hydrogen** (H₂) are the reactants. This reaction requires high pressure and a catalyst to occur efficiently. Ammonia is the resulting product used in the production of fertilizers.