Atoms are rearranged in chemical reactions. The substances that react together are called reactants. The substances that are formed in the reaction are called products.
When talking about particles, reactions and balanced equations, the main principle to be considered is that WHAT GOES IN MUST COME OUT. This means that the mass of the products of a reaction is equal to the mass of the reactants. No atoms are created or destroyed in a chemical reaction. The total mass of the reactants is the same as the total mass of the products. This is called the conservation of matter or, in other words, we could say that the particles in the reactants are simply rearranged to make the new products.
CHEMICAL EQUATIONS
The changes in chemical reactions can be worded using equations. A word equation shows the names of each substance involved in a reaction, and must not include any chemical symbols or formulae. As the atoms that go into a reaction as reactants must come out at the other side at products, the equations must be BALANCED, which means that there must be the same number of atoms on the left and on the right. A balanced equation gives more information about a chemical reaction than a word equation because it includes the symbols and formulae of the substances involved. There are two steps in writing a balanced equation:
1) to replace the name of each substance with its symbol or formula
2) to use numbers to balance the equation, if it is not already balanced