How does the amount of the reactant change during a chemical reaction?

1. A chemical reaction is one in which a substance changes its chemical composition to form a new substance.
2. A general chemical equation can be shown as follows:

$$\begin{gathered} \mathrm{A}+\mathrm{B}\to \mathrm{C}+\mathrm{D} \\ \left(\mathrm{Reactants}\right)\left(\mathrm{Products}\right) \end{gathered}$$

4. There are certain rules that are to be followed for writing a chemical equation. The most important one is the law of conservation of mass.

Law of conservation of matter:

1. This law states that the matter can neither be created nor be lost.
2. Hence, in a reaction, the total mass remains constant. As the reaction proceeds, the amount of reactants keeps decreasing while the amount of product keeps increasing.
3. Hence, the law holds good in this case.