How do chemical equations show reactants and products?

A chemical equation serves as a standardized method for representing the essential features of a chemical reaction using chemical symbols and formulas.1

Structure and Representation

• Placement: By convention, reactants—the substances present at the start of a reaction—are written on the left side, while products—the substances formed at the end—are written on the right.1
• Directionality: A single arrow ($\to$) between the reactants and products denotes an irreversible reaction, whereas a double arrow indicates a reversible reaction.1
• Stoichiometry: Numbers placed before chemical formulas, known as stoichiometric factors, indicate the relative molecular proportions of the substances involved.23

Conservation of Matter

Because matter is neither created nor destroyed in chemical reactions, equations must be balanced. This means the same number of atoms of each element must appear on both sides of the equation. Balancing ensures that the total mass of the reactants equals the total mass of the products, reflecting the law of conservation of matter.31