# What is Law of Conservation of Mass? – Definition, Formula

## Introduction

The law of conservation of mass is a fundamental principle in physics and chemistry that states that the mass of an isolated system remains constant over time, regardless of any physical or chemical changes that occur within the system. This principle was first established by Antoine Lavoisier, a French chemist, in the 18th century.

## What is the Law of Conservation of Mass?

The law of conservation of mass, also known as the principle of mass conservation, can be defined as the principle that mass can neither be created nor destroyed in a chemical reaction or a physical change. In other words, the total mass of substances involved in a reaction or a process before and after remains the same, even if the substances undergo a transformation or change in their physical or chemical properties.

Let’s imagine you have a magical box containing some objects. According to the Law of Conservation of Mass, if you play around with these objects – smashing, squishing, or transforming them – the total mass inside the box will always stay the same. It’s like a superhero power that matter possesses!

## Law of Conservation of Mass Formula

The law of conservation of mass can be mathematically represented using the following formula:

Mass of Reactants = Mass of Products

Also, we can represent as,

Mass (Initial) = Mass (Final)

This equation implies that the total mass of all the reactants involved in a process, or a reaction is equal to the total mass of the products formed. This equation holds true for all types of reactions and processes, whether they are physical or chemical in nature.

Yet, in the realms of fluid mechanics and continuum mechanics, the law of conservation of mass can be expressed through the following equation, utilizing the differential form of the continuity equation:

The mathematical expression of the Law of conservation of mass is,

$$\frac{ \delta \rho }{ \delta t} + \nabla ( \rho v)=0$$

### Law of Conservation of Mass Example

The following are examples of the Law of conservation of Mass.

Example 1:

To illustrate the law of conservation of mass further, let’s consider the burning of a candle. When a candle burns, the wax reacts with oxygen in the air to produce carbon dioxide and water vapor. Despite the visible changes in the candle’s appearance and the formation of new substances, the law of conservation of mass remains intact.

Initially, the candle weighs a certain amount. As it burns, the wax is consumed, and the candle gradually becomes smaller. However, if we were to weigh the products of the reaction, namely the carbon dioxide and water vapor, their total mass would be equal to the initial mass of the candle. This is a clear demonstration of the law of conservation of mass in action.

Example 2:

Let’s understand this concept with another example. Picture a balloon filled with air. Now, if you pop the balloon, the air rushes out. It might seem like the air disappeared but remember our superhero – the Law of Conservation of Mass!

Before the pop, the air was inside the balloon, and after the pop, the air is still there, just not trapped in the balloon anymore. The total mass of the air before and after the pop remains the same, thanks to our superhero law.

## When Matter Undergoes Physical Change?

In the case of physical changes, such as changes in state or phase transitions, the law of conservation of mass holds. For example, when a solid ice cube melts and turns into liquid water, the mass of the water formed is the same as the mass of the ice cube. Similarly, when water vapor condenses and forms liquid droplets, the total mass of the liquid remains the same as the mass of the vapor.

During physical changes, the arrangement or organization of the molecules or atoms may change, but the total number of particles remains constant. This is why the law of conservation of mass applies to these processes.

## When Matter Undergoes Chemical Change?

When matter undergoes a chemical change, such as a reaction between different substances, the law of conservation of mass still holds true. During a chemical reaction, atoms are rearranged to form new molecules and compounds. However, the total number and types of atoms on both sides of the reaction equation remain the same.

For example, when hydrogen gas (H2) reacts with oxygen gas (O2) to form water (H2O) through the well-known reaction, combustion occurs:

2H2 + O2 → 2H2O

In this reaction, the total mass of the hydrogen and oxygen molecules before the reaction is equal to the total mass of the water molecules after the reaction. The law of conservation of mass ensures that no atoms are lost or gained during the reaction.

## Limitation of the Law of Conservation of Mass

While the law of conservation of mass is a fundamental principle in science, it has certain limitations. One limitation is that it assumes a closed system where no mass is exchanged with the surroundings. In reality, it is often challenging to create a perfectly isolated system and small amounts of mass may be lost or gained through interactions with the environment.

Additionally, the law of conservation of mass does not account for the conversion of mass into energy or vice versa, as described by Albert Einstein’s famous equation, E=mc². In nuclear reactions, a small amount of mass can be converted into a large amount of energy, violating the strict conservation of mass.

Despite these limitations, the law of conservation of mass remains a powerful concept that has guided scientific investigations and experiments for centuries.

## Final Notes

The law of conservation of mass is a foundational principle in physics and chemistry that states that the total mass of an isolated system remains constant over time. This principle applies to both physical changes, where the arrangement of particles changes, and chemical changes, where new substances are formed. The law of conservation of mass is mathematically represented by the equation Mass of Reactants = Mass of Products. While the law has its limitations, it serves as a crucial tool in analyzing and understanding various processes and reactions in the natural world.

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## FAQ’s

Q: What is the state of the Law of Conservation of Mass?

The Law of Conservation of Mass states that the total mass of a closed system remains constant over time, regardless of the processes occurring within that system.

Q: Why is there no change in mass during chemical reactions?

During chemical reactions, substances transform into new ones, but the total mass remains the same. This is because the Law of Conservation of Mass ensures that matter cannot be created or destroyed; it can only change its form.