Definition

The law of conservation of mass states that mass can neither be created nor destroyed during a chemical reaction. The total mass of the reactants is equal to the total mass of the products.

Explanation

During a chemical reaction, atoms rearrange to form new substances. No atoms are created or destroyed, so the total mass remains constant.

Example

When hydrogen reacts with oxygen, water is formed.

\[ 2H_2 + O_2 \rightarrow 2H_2O \]

In this reaction, the total mass of hydrogen and oxygen before the reaction is equal to the mass of water formed after the reaction.

Important Points

• Reactants are the substances that take part in a chemical reaction.

• Products are the new substances formed during a chemical reaction.

• Atoms are rearranged during a chemical reaction.

• The total mass of reactants is equal to the total mass of products.

• In a closed system, mass remains constant even when a gas is produced.