Short Answer

Charles’s Law states that the volume of a gas is directly proportional to its temperature when the pressure and amount of gas are kept constant. This means that when the temperature of a gas increases, its volume also increases, and when the temperature decreases, the volume decreases.

Charles’s Law explains many real-life situations. For example, a balloon expands when heated because the gas inside it expands. Similarly, during cold weather, car tyres appear slightly deflated because the gas inside contracts as temperature drops.

Detailed Explanation :

Charles’s Law

Charles’s Law is an important gas law in chemistry that explains how gases expand or contract when their temperature changes. It was discovered by Jacques Charles, a French scientist, in the late 18th century. The law shows the relationship between volume and temperature of a fixed amount of gas at constant pressure.

According to Charles’s Law, if the temperature of a gas increases, its volume increases, and if the temperature decreases, its volume decreases. The change in volume happens because gas particles gain or lose kinetic energy with changes in temperature. Since gases are highly expandable, changes in temperature have strong effects on their volume.

Charles’s Law is widely used in daily life, scientific experiments, aviation, weather studies, and engineering. It helps explain how gases behave under different temperature conditions.

Statement and Mathematical Form

Charles’s Law is stated as:

“The volume of a fixed mass of gas is directly proportional to its temperature (in Kelvin) at constant pressure.”

The relationship can be written as:
V ∝ T
or
V / T = constant

Where:
V = Volume of gas
T = Temperature in Kelvin (K)

To compare initial and final states, the formula is:
V₁ / T₁ = V₂ / T₂

This equation helps calculate how gas volume changes with temperature.

Why Charles’s Law Works

The law can be explained using kinetic theory. Gas particles move in all directions with constant, random motion. Temperature is a measure of the average kinetic energy of particles.

• When temperature increases, gas particles move faster and need more space. This causes the gas to expand, increasing its volume.
• When temperature decreases, particles move slowly and occupy less space, so the volume decreases.

Pressure must remain constant for Charles’s Law to apply. If pressure changes, the gas will behave differently.

Understanding Temperature in Kelvin

Charles’s Law uses Kelvin because it is an absolute temperature scale and avoids negative values.
The formula to convert Celsius to Kelvin is:
K = °C + 273

Example:
27°C = 27 + 273 = 300 K

Using Kelvin ensures accurate calculations for volume–temperature relationships.

Graphical Representation

A graph of Volume (V) vs Temperature (T) gives a straight line.
This straight line shows that volume increases as temperature increases.

The line touches the temperature axis at −273°C, which is known as absolute zero, the lowest possible temperature. At absolute zero, gas particles would theoretically stop moving.

Real-Life Applications of Charles’s Law

Charles’s Law explains many everyday situations where temperature affects the behaviour of gases.

1. Hot Air Balloons

When air inside the balloon is heated:

• Temperature increases
• Volume increases
• Balloon rises because warm air becomes lighter

2. Balloons in Different Temperatures

A balloon expands in warm air and shrinks in cold air.
This happens due to changes in gas volume with temperature.

3. Car Tyres

In winter, tyre pressure drops because the air inside contracts due to low temperature.
In summer, pressure increases due to expansion.

4. Breathing

When air goes into the lungs, it warms up and expands, helping the lungs fill properly.

5. Spray Cans

Warm temperatures increase gas volume and pressure inside cans, which is why they should not be placed near heat.

6. Weather and Climate

Warm air expands and rises, creating atmospheric movements that lead to winds and clouds.

Importance of Charles’s Law in Science

Charles’s Law helps in:

• designing engines and air pumps
• understanding atmospheric behaviour
• predicting gas expansion in experiments
• studying thermodynamics
• designing equipment for temperature-sensitive gases

It also forms the foundation for the combined gas law and the ideal gas equation, which are used in advanced chemistry.

Limitations of Charles’s Law

Charles’s Law applies accurately only for:

• ideal gases
• moderate temperatures
• constant pressure conditions

At extremely high or low temperatures, real gases may deviate from the law.

Conclusion

Charles’s Law explains the direct relationship between the volume of a gas and its temperature at constant pressure. When temperature increases, gas particles move faster, causing the volume to increase; when temperature decreases, the volume reduces. This law is essential in understanding everyday phenomena like hot air balloons, tyre pressure changes, and weather patterns. Charles’s Law remains a key principle in chemistry, physics, and real-world applications.