Question

Fill in the blanks: In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called ..................…

Answer 1

Law of conservation of mass:

1. According to this law, the mass of the reactants and the mass of the products remains the same for a low-energy thermodynamic process.
2. In an isolated system, mass cannot be generated or destroyed, but it may be converted from one form to another.
3. Example: Coal combustion turns the Carbon atom (C) into Carbon dioxide (${\mathrm{CO}}_2$) molecule.
4. A Carbon atom changes from a solid structure to gas, but its mass does not change.
5. Here, the Carbon atom is a reactant, and when it burns, it becomes Carbon dioxide, but its mass does not change.
6. Carbon's atomic mass is 12, and Oxygen's atomic mass is 16; when it becomes Carbon dioxide the total mass is 28, which is equal to the reactant's mass.

Hence, in a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called the Law of conservation of mass.