The Law of Conservation of Mass, also known as the Law of Lavoisier, is a fundamental law in chemistry that states that the total mass of the reactants in a chemical reaction is equal to the total mass of the products. This law implies that matter cannot be created or destroyed in chemical reactions, but only rearranged or combined in different forms.

Chemical equations, also known as balanced chemical equations, are symbolic representations of chemical reactions. They use chemical formulas to show the reactants, products, and their relative amounts involved in a chemical reaction.

The law of conservation of mass is closely related to the concept of balancing chemical equations, where coefficients are used to adjust the stoichiometric ratios of reactants and products to ensure that the total mass on both sides of the equation is equal. Coefficients represent the relative number of molecules, moles, or formula units of each substance involved in the reaction.

To balance a chemical equation, coefficients are placed in front of the chemical formulas, not as subscripts within the formulas. Coefficients are added without altering the chemical formulas or subscripts. Balancing ensures that the total mass of the reactants is equal to the total mass of the products.

For example, consider the following unbalanced chemical equation for the combustion of methane:

CH₄ + O₂ → CO₂ + H₂O

To balance this equation, we need to add coefficients to ensure that the number of atoms of each element is equal on both sides of the equation. We start by balancing the carbon atoms: since there is one carbon atom on the left side and one carbon atom on the right side, no coefficients are needed for CH₄ and CO₂.

Next, we balance the hydrogen atoms: there are four hydrogen atoms on the left side and two hydrogen atoms on the right side. To balance this, we need to place a coefficient of 2 in front of the H₂O molecule:

CH₄ + O₂ → CO₂ + 2 H₂O

Now, we balance the oxygen atoms: there are two oxygen atoms on the left side and four oxygen atoms on the right side. To balance this, we need to place a coefficient of 2 in front of the O₂ molecule:

CH₄ + 2 O₂ → CO₂ + 2 H₂O

By adding these coefficients, we've ensured that the total mass of the reactants (CH₄ and 2 O₂) is equal to the total mass of the products (CO₂ and 2 H₂O), satisfying the law of conservation of mass.

In summary, the law of conservation of mass is a fundamental principle that requires the total mass of reactants in a chemical reaction to be equal to the total mass of products. This concept is directly reflected in balancing chemical equations, where coefficients are adjusted to ensure that the number of atoms of each element is equal on both sides, thereby maintaining the overall mass balance of the reaction.