Reactants
The substances that are present at the start of a chemical reaction. Reactants are written on the left side of a chemical equation, before the arrow.
Products
The substances formed as a result of a chemical reaction. Products are written on the right side of the equation, after the arrow.
Law of Conservation of Mass
Matter cannot be created or destroyed in a chemical reaction. The total mass of reactants always equals the total mass of products. This is why chemical equations must be balanced ā the same number of each type of atom must appear on both sides.
Real-life example: When wood burns, it seems to disappear ā but the carbon and hydrogen atoms have simply converted into carbon dioxide and water vapour that escape into the air.