Why are chemical equations balanced according to the law of conservation of mass?

Chemical equations are balanced according to the law of conservation of mass to ensure that no atoms are lost or created during a reaction.

The law of conservation of mass, also known as the principle of mass conservation, states that the total mass of substances in a closed system will remain constant, regardless of the processes acting inside the system. This means that in a chemical reaction, the total mass of the reactants (the substances that start the reaction) must equal the total mass of the products (the substances that are produced by the reaction).

When we balance a chemical equation, we are essentially making sure that the number of atoms of each element in the reactants side is equal to the number of atoms of the same element in the products side. This is because, according to the law of conservation of mass, atoms are neither created nor destroyed in a chemical reaction. They are simply rearranged.

For example, consider the reaction between hydrogen and oxygen to form water. The unbalanced equation is H2 + O2 → H2O. If we count the atoms, we see that there are 2 hydrogen atoms and 2 oxygen atoms on the reactants side, but only 2 hydrogen atoms and 1 oxygen atom on the products side. To balance the equation, we need to adjust the number of water molecules produced, so that there are the same number of oxygen atoms on both sides. The balanced equation is 2H2 + O2 → 2H2O. Now, there are 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation, which is in accordance with the law of conservation of mass.

Balancing chemical equations is a fundamental skill in chemistry. It not only ensures that we are following the law of conservation of mass, but also allows us to predict the quantities of reactants needed or products formed in a chemical reaction.