Chemical Reaction
A chemical reaction is a process in which one or more substances (reactants) are transformed into one or more different substances (products) through the breaking and forming of chemical bonds. Chemical reactions involve changes in the arrangement of atoms, resulting in new materials with different properties from the original substances. They are fundamental to all biological, industrial, and environmental processes, from cellular respiration to the manufacture of medicines.
Common Signs That a Chemical Reaction Has Occurred
| Observation | Example | Explanation |
|---|---|---|
| Colour change | Iron turning red-brown | Formation of iron oxide (rust) |
| Gas production | Fizzing when vinegar meets baking soda | CO₂ gas is released |
| Precipitate forms | White solid in lead nitrate + KI solution | Insoluble product formed |
| Temperature change | Hand warmers heating up | Exothermic reaction releases heat |
| Light emission | Burning magnesium ribbon | Energy released as visible light |
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Related Terms
Reactant
A reactant (also called a reagent) is any substance that enters into and is altered in the course of a chemical reaction, written on the left-hand side of a chemical equation. Reactants supply the atoms that are rearranged to form products, and their amounts determine how much product can be formed. The concept of a limiting reactant is especially important in industrial chemistry, where maximising product yield while minimising waste requires precise control of reactant quantities.
Chemical Product
A chemical product is a substance formed as a result of a chemical reaction, written on the right-hand side of a chemical equation after the arrow. Products have different chemical properties and structures compared to the reactants from which they originate, because chemical bonds have been broken and reformed in new arrangements. Understanding products is essential for predicting reaction outcomes, designing syntheses of useful materials, and assessing environmental impacts of chemical processes.
Balancing Chemical Equations
Balancing chemical equations is the process of adjusting the stoichiometric coefficients in front of each formula in a chemical equation so that the number of atoms of each element is equal on both the reactant and product sides, satisfying the Law of Conservation of Mass. Only coefficients (not subscripts) may be changed during balancing, because altering subscripts would change the identity of the compounds. Balanced equations are essential for calculating the exact quantities of reactants and products in stoichiometric calculations used in laboratories and industry.
From Latin "reactio" meaning "a response or action in return", combining "re-" (again, back) and "agere" (to act). The term entered chemistry in the 17th century as scientists began systematically studying transformations of matter.