The law of conservation of mass, also known as the principle of mass conservation, says that the mass of any system closed to all transfers of matter and energy must remain constant over time, because mass cannot change and hence quantity cannot be added or subtracted. As a result, the amount of mass is conserved through time.

In several domains, such as chemistry, mechanics, and fluid dynamics, the principle of mass conservation is commonly applied. Mikhail Lomonosov independently demonstrated mass conservation in chemical reactions, which was later rediscovered by Antoine Lavoisier in the late 18th century. The establishment of this law was fundamental in the transition from alchemy to contemporary chemistry as a scientific science.

The Law of Conservation of Mass

The concept of conservation of mass states that no matter how the constituent elements rearrange themselves, the mass of an entity or collection of entities remains constant. In physics, mass has been viewed in two ways that are mutually consistent. On the one hand, it is seen as a measure of inertia, or the resistance that free bodies provide to forces: trucks are more difficult to move and stop than smaller automobiles. On the other side, mass is thought to cause gravitational force, which is responsible for an object’s weight: trucks are heavier than cars. The two approaches to mass are widely regarded as comparable. The concept of conservation of mass states that no matter how the constituent elements rearrange themselves, the mass of an entity or collection of entities remains constant. In physics, mass has been viewed in two ways that are mutually consistent. 

On the one hand, it is seen as a measure of inertia, or the resistance that free bodies provide to forces: trucks are more difficult to move and stop than smaller automobiles. On the other side, mass is thought to cause gravitational force, which is responsible for an object’s weight: trucks are heavier than cars. The two approaches to mass are widely regarded as comparable.

According to the concept of mass conservation, different measurements of an object’s mass taken under different circumstances should always be the same, whether measured inertially or gravitationally.

Conservation of Mass Formula

In fluid mechanics and continuum mechanics, the law of conservation of mass can be stated in differential form using the continuity equation as:

∂ρ/ ∂t+ ∇(ρv)=0

Here,

ρ= Density

t= Time

v= Velocity

= Divergence

Everyday Examples of Conservation of Mass

There are several instances in nature that can be used to demonstrate this principle. Some of the most basic examples are provided below to help you understand how to apply the law in everyday situations.

• Example 1: When you burn charcoal, you get soot, ashes, heat, and a variety of gases as a result of the burning. These combustion products are now directly proportional to the raw material or charcoal that was burned, so that the charcoal converts into all of the products while the mass remains unchanged. When mass is converted, however, a small amount of energy is produced, which in this case is heat energy. However, because these changes are minor and difficult to detect, they are not taken into account.
• Example 2: In this example, we’ll look at a very basic chemical reaction involving 1 hydrogen molecule and 112 oxygen molecules. When these two molecules react in the presence of heat, one molecule of water (H2O) is produced. Hydrogen has a molecular weight of 2 and Oxygen has a molecular weight of 8, which when combined yields 10 units, which is the molecular weight of the water molecule. As a result, in chemistry, the mass of the substrates in the products is kept constant.

History of the Law of the Conservation of Mass

The concept of mass underwent a fundamental reworking with the introduction of relativity theory in 1905. The absoluteness of mass has been gone. The mass of an object was discovered to be equivalent to energy, interconvertible with energy, and to increase dramatically at speeds approaching those of light. The total energy of an object was formerly thought to include both its rest mass and the mass increase generated by high speed. It was observed that the rest mass of an atomic nucleus is significantly less than the total of the rest masses of its constituent neutrons and protons. Mass was no longer thought to be constant or immutable.

Both chemical and nuclear reactions involve some conversion of rest mass to energy, resulting in products that are smaller or larger in mass than the reactants. For common chemical reactions, the difference in mass is sufficiently small that mass conservation may be used as a practical concept for estimating product mass. The behaviour of masses actively participating in nuclear reactors, particle accelerators, and thermonuclear events in the Sun and stars, however, defies mass conservation. The conservation of mass-energy is the new conservation principle.

Conclusion

Chemical reactions and physical transformations do not create or remove mass in an isolated system, according to the law of conservation of mass. According to the law of conservation of mass, the mass of the products of a chemical reaction must equal the mass of the reactants. The law of conservation of mass can be used to solve for unknown masses, such as how much gas is consumed or created during a process.