Reactants are the chemical substances that are used by chemists to create new substances, or the substances that are present before a chemical reaction takes place. They are written on the left hand side of the arrow in a chemical reaction.
In the chemical reaction Ca CO3 + 2HCl → CaCl2 + H2O + CO2↑, calcium carbonate (Ca CO3) and hydrochloric acid (HCl) are the two reactants. In terms of mole, this equation is described as, one mole of calcium carbonate reacts with two moles of hydrochloric acid to give one mole of calcium chloride, one mole of water and carbon dioxide gas.
Products are the substances obtained as a result of a chemical change. The products are conventionally written on the right hand side of the arrow. In the chemical reaction CaCO3 + 2HCl → CaCl2 + H2O + CO2↑, calcium chloride (CaCl2), water (H2O) and Carbon dioxide (CO2) are the products. Physical state is not necessarily maintained during a chemical reaction, which means solid reactants can form liquid or gaseous products.