# Law of Conservation of Mass

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## Introduction :

The law of conservation of mass is a fundamental principle in physics and chemistry which states that in any closed system, the mass of the system remains constant over time. In other words, the total amount of mass in a closed system before and after a physical or chemical change remains the same.

It is important to note that the law of conservation of mass applies only to closed systems, where there is no exchange of matter with the surrounding environment. In open systems, mass can be lost or gained through interactions with the environment, and the law of conservation of mass does not apply

## What is Law of Conservation of Mass

The law of conservation of mass is based on concept, the matter cannot be created or destroyed, only transformed from one form to another form.

For example, in a chemical reaction, the total mass of the reactants must be equal to the total mass of the products. This means that the amount of matter on the reactant side of the equation must be the same as the amount of matter on the product side.

The law of conservation of mass can be expressed in the form of a continuity equation in the mechanics of fluids and continuum mechanics. This equation is as follows::

Where,

ρ = density
t = time
v = velocity
= divergence

## Physical Change in Law of Conservation of Mass

In the Law of Conservation of Mass, a physical change is a process in which the properties of a substance change without any change in its chemical composition. In a physical change, the total mass of the substance remains the same before and after the change, since there is no change in the number of atoms or molecules involved

Example:

Ice      → Heat    → Water

(solid)                    (Liquid)

Examples of physical changes include changes in state, such as melting, freezing, boiling, and condensation, as well as changes in shape, size, or volume. For instance, when an ice cube melts, it undergoes a physical change from a solid to a liquid state, but the total mass of the water remains the same.

## Chemical Change in Law of Conservation of Mass

In the Law of Conservation of Mass, a chemical change is a process in which one or more substances are transformed into one or more new substances with different chemical properties. In a chemical change, the total mass of the reactants must be equal to the total mass of the products, since no mass is created or destroyed during the reaction.

### NaOH + HCl → NaCl + H2O

#### Reactants:

1 molecule of NaOH = 22.99 + 16 + 1.01 = 40 g/mol

1 molecule of HCl = 1.01 + 35.45 = 36.46 g/mol

Total mass of reactants = 40 + 36.46 = 76.46 g/mol

#### Products:

1 molecule of NaCl = 22.99 + 35.45 = 58.44 g/mol

1 molecule of H2O = 2(1.01) + 16 = 18.02 g/mol

Total mass of products = 58.44 + 18.02 = 76.46 g/mol

As we can see, the total mass of the reactants (76.46 g/mol) is equal to the total mass of the products (76.46 g/mol), demonstrating the Law of Conservation of Mass. No matter is created or destroyed in this reaction, and the total mass of the system remains constant.

## Combustion Process

#### Combustion is a chemical reaction that occurs when a fuel combines with oxygen to produce heat and light. The combustion process involves a series of steps that can be summarized as follows:

Ignition: The process of combustion begins with the ignition of the fuel, which can be initiated by a spark or a flame.

Heating: The heat from the ignition source raises the temperature of the fuel to its ignition point, which is the temperature at which it will combust.

Combustion: Once the fuel has reached its ignition point, it reacts with oxygen to produce carbon dioxide, water vapor, and other combustion byproducts, depending on the type of fuel.

Heat release: The combustion reaction releases heat and light, which can be harnessed for various applications, such as powering engines or generating electricity.

Exhaust: The combustion byproducts are expelled from the combustion chamber as exhaust gases.

#### The combustion process can be illustrated using the example of burning gasoline in an internal combustion engine:

Ignition: A spark plug ignites the gasoline vapor in the engine's combustion chamber.

Heating: The heat from the spark raises the temperature of the gasoline to its ignition point.

Combustion: The gasoline combines with oxygen from the air to produce carbon dioxide, water vapor, and other combustion byproducts.

Heat release: The heat and pressure from the combustion drive the engine's pistons, which generate mechanical energy that can be used to power the vehicle.

Exhaust: The exhaust gases, including carbon dioxide and other combustion byproducts, are expelled from the engine through the exhaust system.

## Law of Conservation of Mass Examples

### Example:

Firstly Take a container and place 16 g of methane or CH4 and 64 g of O2. After the container is closed, CH4 and O2 remain closely packed. Now, ad the reaction proceeds, i.e., the combustion reaction, we get the following products:

The combustion of methane with oxygen produces carbon dioxide (CO2) and water vapor (H2O) according to the following balanced chemical equation:

CH4 + 2O2 → CO2 + 2H2O

Calculate the moles of methane and oxygen:

Moles of CH4 = 16 g

Moles of O2 = 64 g

the total mass of reactants was:  16 + 64 = 80 g

44 +  mass of H2O = 80 g

we get the mass of 2 moles of H2O as 36 g.

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