What is Boyle’s Law?

Short Answer

Boyle’s Law states that the pressure of a gas is inversely proportional to its volume when the temperature and amount of gas remain constant. This means that if the volume of a gas decreases, its pressure increases, and if the volume increases, its pressure decreases.

This law helps explain many real-life situations, such as how syringes work, how balloons expand, and how air behaves in scuba diving tanks. Boyle’s Law forms the foundation for understanding the behaviour of gases under pressure.

Detailed Explanation :

Boyle’s Law

Boyle’s Law is one of the fundamental gas laws in chemistry that explains how the pressure of a gas changes when its volume changes at constant temperature. It was discovered by the scientist Robert Boyle in the 17th century. The law describes the relationship between pressure and volume for a fixed amount of gas kept at a constant temperature.

According to Boyle’s Law, when the volume of a gas decreases, its pressure increases, and when the volume increases, the pressure decreases. This relationship works only when the temperature and the quantity of gas do not change. The law is based on the idea that gas particles are constantly in motion and collide with the walls of their container, creating pressure.

Statement and Mathematical Form

Boyle’s Law is stated as:

“The pressure of a fixed amount of gas is inversely proportional to its volume at constant temperature.”

This means:

  • If volume ↓, pressure ↑
  • If volume ↑, pressure ↓

The mathematical form of the law is:
P ∝ 1/V
or
P × V = constant

Where,
P = Pressure of gas
V = Volume of gas

If the initial and final conditions are compared, the equation becomes:
P₁V₁ = P₂V₂

This equation helps in solving numerical problems related to gases.

Why Boyle’s Law Works

Boyle’s Law can be explained using the kinetic theory of gases. Gas particles move in all directions and constantly collide with the walls of the container. These collisions produce pressure. When the volume of the container decreases:

  • Gas particles have less space to move
  • Collisions with walls become more frequent
  • Pressure increases

When the volume increases:

  • Gas particles have more room to move
  • Collisions become less frequent
  • Pressure decreases

This behaviour matches the law perfectly.

Graphical Representation

Boyle’s Law can be shown on a graph:

  • A graph of Pressure (P) vs Volume (V) gives a curve.
  • A graph of Pressure (P) vs 1/Volume (1/V) gives a straight line.

These graphs help understand the inverse relationship between pressure and volume.

Real-Life Applications of Boyle’s Law

Boyle’s Law plays an important role in many daily and industrial processes.

  1. Syringes

When the plunger is pulled back, the volume inside the syringe increases and pressure decreases. This causes fluid to enter. When the plunger is pushed, volume decreases and pressure increases, pushing fluid out.

  1. Balloons

When air is blown into a balloon, pressure inside increases and volume expands until balanced with external pressure.

  1. Human Breathing

During inhalation:

  • Lungs expand (volume ↑)
  • Pressure inside lungs ↓
  • Air enters

During exhalation:

  • Lungs contract (volume ↓)
  • Pressure ↑
  • Air is pushed out
  1. Scuba Diving

Underwater pressure increases with depth. Boyle’s Law helps divers understand how air in their tanks behaves and how their lungs respond to pressure changes.

  1. Air Pumps

When a pump handle is pushed, air volume reduces and pressure increases, forcing air into tyres.

  1. Storage of Gases

Gases like LPG and oxygen are compressed to smaller volumes in cylinders by increasing pressure.

Importance of Boyle’s Law in Science

Boyle’s Law is important because it:

  • Helps predict gas behaviour during compression and expansion
  • Forms the basis of gas equations and kinetic theory
  • Plays a key role in the study of thermodynamics
  • Helps design machines, pumps, and storage cylinders

Understanding Boyle’s Law makes it easier to study other gas laws such as Charles’s Law and Gay-Lussac’s Law.

Limitations of Boyle’s Law

Boyle’s Law works best for:

  • Ideal gases
  • Low pressures
  • Moderate temperatures

At very high pressures or very low temperatures, gases do not behave ideally, and the law may not hold exactly.

Conclusion

Boyle’s Law describes the inverse relationship between the pressure and volume of a gas at constant temperature. When volume decreases, pressure increases, and when volume increases, pressure decreases. This law is fundamental in understanding gas behaviour in various scientific, industrial, and everyday processes. From breathing to using syringes and pumps, Boyle’s Law helps explain many natural and practical situations. It remains an essential part of chemistry and physics.