Chemical reaction

A chemical reaction is a change in which a substance loses its characteristics and becomes one or more new substances.

Equation
A chemical reaction is represented by an equation using chemical formulas, chemical symbols, and coefficients.



Terms
Reactant - an element or compound that undergoes chemical change and is usually written to the left of the arrow in a chemical equation.

Product - an element or compound that is produced from a chemical change and is usually written to the right of the arrow in a chemical equation.

Coefficient - a number that appears in front of a chemical formula and indicates how many units of that substance are present.

Subscript - a number written at the lower right of a chemical symbol in a formula to indicate the number of components immediately preceding it.

Oxidation number - a number that reflects the charge that an atom in a compound would have if all the bonding electrons were arbitrarily assigned to the most electronegative element.

Catalyst - a substance that changes a reaction rate without being permanently changed by the reaction.

Symbols
+ is placed between the formulas of individual reactants and products.

→ means 'yields' or 'produces'; separates reactants from products.

= is the same as arrow.

(aq) - indicates that the reactant or product is in aqueous solution (dissolved in water).

(g) indicates a gaseous reactant or product.

(s) indicates a solid reactant or product.

(l) indicates a liquid reactant or product.

Oxidation and Reduction
Redox reactions are chemical reactions in which one substance surrenders electrons to another. Redox is the common abbreviated form of the name, which is more formally known as an oxidation-reduction reaction. The reactions that take place in all electrochemical cells, or "batteries," are redox reactions. So, too, are all electrolytic reactions.