The Law of Conservation of Mass in a Chemical Reaction

Our Objective

To verify the Law of Conservation of Mass during a chemical reaction.

The Theory 

What is meant by a chemical reaction?

A chemical reaction is process by which one set of chemical substances is transformed to another. There are different types of chemical reactions such as:

  • Acid-base Reactions
  • Precipitation Reactions
  • Synthesis Reactions
  • Oxidation-Reduction Reactions
  • Displacement Reactions
  • Decomposition Reactions   

Substances which chemically react are called reactants and the newly formed substances are called products.
A French chemist, Antoine Lavoisier, who is known as the father of modern chemistry, changed chemistry from a qualitative to a quantitative science. He proved that the mass of the products in a chemical reaction is equal to the mass of the reactants. There are no more atoms at the end of the chemical reaction than there were at the beginning.

The Law of Conservation of Mass states that matter can neither be created nor destroyed in a chemical reaction.


  • Consider the formation of water molecule. Hydrogen combines with oxygen to form  a water molecule.


In this case, the total mass of the reactants = total mass of the products. Also, the number of atoms of hydrogen and oxygen in the reactants side and the products side are equal.

  • Carbon combines with oxygen at low concentration to form carbon monoxide.

In this case, the total mass of reactants and products also are equal. The number of atoms at the beginning and at the end is equal as well.

  •  Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water.

In this case, total mass of reactants = total mass of products.

Learning outcomes

  • Students understand “The Law of Conservation of Mass”.
  • Students acquire the skill to verify the Law of Conservation of Mass.
  • Students identify the chemicals required for the verification of the Law of Conservation of Mass.
  • Students will be able to do the experiment quicker and more accurately in the real lab after understanding the different steps.