What is Boyle’s law?

Short Answer

Boyle’s law states that at a constant temperature, the pressure of a gas is inversely proportional to its volume. This means when the volume of a gas decreases, its pressure increases, and when the volume increases, its pressure decreases. The law applies to gases kept at a constant temperature.

Boyle’s law helps explain many everyday situations such as how air pumps work, why balloons expand or shrink, and how syringes function. It shows that gas pressure changes because gas particles collide more or less frequently with container walls depending on the available space.

Detailed Explanation

Boyle’s Law

Boyle’s law is one of the fundamental gas laws that explains the relationship between the pressure and volume of a gas. This law is named after the scientist Robert Boyle, who studied the behaviour of gases. According to Boyle’s law, when the temperature of a gas is kept constant, the pressure of a gas varies inversely with its volume. In simple words, if the volume decreases, the pressure increases, and if the volume increases, the pressure decreases.

This law helps us understand how gases behave when their space is changed. Gas particles move randomly and collide with the walls of their container. These collisions create pressure. When the space available to the gas becomes smaller, gas particles collide with the walls more frequently, increasing the pressure. When space increases, collisions become less frequent, reducing the pressure.

Inverse Relationship Between Pressure and Volume

The key idea of Boyle’s law is the inverse relationship. This means pressure and volume move in opposite directions when temperature remains constant. If volume doubles, pressure becomes half. If volume becomes half, pressure doubles. This happens because the number of gas particles stays the same, but the space available to them changes.

For example, when you squeeze a balloon, you reduce its volume. As a result, the pressure inside increases because the particles hit the balloon walls more often. When you let go, the balloon expands, increasing volume and reducing pressure.

Why Boyle’s Law Works

Boyle’s law works because of the way gas particles move. Gas molecules are constantly moving and colliding with each other and the walls. These collisions cause pressure.

When the volume decreases:

  • Gas particles are pushed closer.
  • They collide more often with the container walls.
  • More collisions create higher pressure.

When the volume increases:

  • Particles spread out.
  • Collisions become less frequent.
  • Fewer collisions create lower pressure.

Since temperature is constant, the kinetic energy of particles does not change. Only the space changes, which affects how often particles collide.

Role of Constant Temperature

Boyle’s law applies only when temperature remains constant. Temperature affects the speed of particles. If temperature increased, particles would move faster, and the relationship between pressure and volume would change. To study only the effect of volume on pressure, Boyle kept temperature unchanged. This is why the law states “at constant temperature.”

Mathematical Form of Boyle’s Law

Boyle’s law can be written as:
P ∝ 1/V (Pressure is inversely proportional to volume)

Or,
P₁V₁ = P₂V₂, where:

  • P₁ = initial pressure
  • V₁ = initial volume
  • P₂ = final pressure
  • V₂ = final volume

This equation shows that when one value changes, the other adjusts so that the product remains constant.

Everyday Examples of Boyle’s Law

Boyle’s law is involved in many common activities:

  1. Breathing:
    When we inhale, our chest expands, increasing the volume of the lungs. This lowers pressure inside, and air enters.
    When we exhale, lung volume decreases, pressure increases, and air leaves.
  2. Syringes:
    Pulling the plunger increases volume inside the syringe, reducing pressure, and allowing liquid to enter. Pushing the plunger decreases volume, increasing pressure, and forcing the liquid out.
  3. Balloons:
    When you squeeze a balloon, the volume decreases, increasing internal pressure. When you release it, the balloon expands again.
  4. Air Pumps:
    In pumps, decreasing the volume inside the chamber increases pressure, forcing air into tyres.
  5. Scuba Diving:
    At deeper levels underwater, external pressure increases, reducing the volume of air in the diver’s lungs or equipment.

These examples show how Boyle’s law is important in real life.

Scientific Importance

Boyle’s law is one of the basic gas laws used in chemistry, physics, engineering, and medicine. It helps in designing engines, pumps, and safety devices. It also explains natural processes like atmospheric pressure changes and helps scientists understand gas behaviour under controlled conditions.

Conclusion

Boyle’s law states that at constant temperature, the pressure of a gas is inversely proportional to its volume. This means that decreasing the volume increases pressure and increasing the volume decreases pressure. The law is based on the movement and collisions of gas particles and is widely observed in everyday activities such as breathing, balloon inflation, and using syringes. Boyle’s law is essential for understanding how gases behave when their space changes.