Law of Conservation of Mass: Overview, Questions, Preparation

Updated on Sep 1, 2021 04:26 IST

What is the law of conservation of mass?

In 1789, the discovery of the law on mass conservation was attributed to a French physicist, Antoine Lavoisier. The law on the conservation of mass makes it clear that the mass is not produced or destroyed by chemical reactions or physical transformations in an isolated system. In a chemical reaction, the mass of the products must match the mass of the reactants.

Table of Contents

Assumptions behind the law of conservation of mass
What is the equation of Law of Conservation of Mass?
How does it work?
Illustrated examples
FAQs on Law of Conservation of Mass

Assumptions behind the law of conservation of mass

A few assumptions were made to distinguish mass conservation from classical mechanics. Later, with the help of quantum mechanics and special relativity, the law of mass conservation was changed to make energy and mass one retained quantity.

What is the equation of Law of Conservation of Mass?

The law of conservation of mass can be presented in the differential form using the continuity equation in fluid mechanics and continuum mechanics as below.

∂ρ➗∂t+▽(ρv)=0

where,

ρ stands for the density
t stands for the time
v stands for the velocity
▽ stands for the divergence

How does it work?

Combustion process: Burning of sticks is a conservation of mass as the burning of wood sticks involves oxygen, carbon dioxide, water vapour and ashes. If we count the total mass of the wooden sticks and the oxygen before setting the wood sticks on fire, we will discover that this mass is close to the mass of the ashes, the carbon dioxide and the water vapours added together. In this example of sticks burning, we learn here that no matter and therefore no mass is lost through the process of burning. That example proves that mass is neither created nor destroyed.

The law on the conservation of mass states that the matter cannot be produced or destroyed. Only the structure can be altered. In an isolated system, the amount, or mass, of matter will still be constant, irrespective of any chemical reactions or physical changes taking place. The law of conservation of mass in chemistry shows that the mass of the products in a chemical reaction will always equal the reactants of the reaction. In chemistry, this law is relevant, particularly when combining various materials and testing the reactions between them.

This chapter has 3% weightage in 11th standard class exam.

Illustrated examples

Combustion process.
Burning of sticks is a conservation of mass as the burning of wood sticks involves oxygen, carbon dioxide, water vapour and ashes.
Gas vapours.

FAQs on Law of Conservation of Mass

Q. What is the Law of Conservation of Chemistry?

A. Sir Antoine Lavoisier's discovery in 1789 explains that mass is neither created nor destroyed by chemical reactions. In other words, the mass of any element at the beginning of the reaction is equal to the mass of that element at the end of the reaction.

Q. What is the law of conservation of energy in easy words?

A. This law, first proposed and tested by Émilie du Châtelet, is all about how energy cannot be created or destroyed; rather, it can only be transformed or transferred from one form to another.

Q. What is an easy definition of the law on the conservation of mass?

A. Mass never gets produced or destroyed because of chemical reactions or physical transformations. The law on mass conservation explains that the mass of the products must be equal to the mass of the reactants in the chemical reaction.

Q. Why is it problematic to prove the law of conservation of mass?

A. When a gas is produced, it is tough to verify the law of mass conservation because the gas molecules pass rapidly into and away from the airspace.