Short Answer

Gases exert pressure on the walls of a container because their particles move very fast in all directions. When these fast-moving particles hit the walls of the container, they apply a force. The total force of many collisions on a particular area creates pressure.

Since gas particles are far apart and move freely, they collide with the walls continuously. More collisions mean more pressure. This is why heating a gas increases pressure, and compressing a gas also increases the number of collisions inside the container.

Detailed Explanation :

Why Gases Exert Pressure on the Walls of the Container

Gases behave differently from solids and liquids because their particles move freely and rapidly in all directions. One of the most important properties of gases is that they exert pressure on the walls of any container in which they are kept. This pressure is not caused by pushing or squeezing from outside; it is created from inside due to the movement of gas particles. The pressure exerted by a gas explains many everyday situations, such as inflated balloons, air pumps, pressure cookers, and the movement of air.

Understanding why gases exert pressure requires us to think at the particle level. Gas particles are in constant motion, and their collisions with the container walls produce a force. When this force acts over a surface area, pressure is formed.

How Gas Particles Create Pressure

1. Gas Particles Move Rapidly

Gas particles have high kinetic energy, which means they are always moving at high speed. Unlike solids and liquids, they do not stay close together. Because of this fast and free movement, gas particles travel quickly until they hit something—either another particle or the wall of the container.

This high-speed movement is the reason gases can fill any available space.

2. Collisions With Container Walls

When gas particles hit the walls of a container, they exert a force on the wall. These collisions are continuous and occur in all directions.

• Each collision applies a small force.
• Many collisions happening every second produce a noticeable force.
• This force per unit area is called gas pressure.

If there were no movement or collisions, the gas would not exert pressure.

3. Number of Collisions Determines Pressure

The pressure inside the container depends on how often and how forcefully the particles hit the walls.

More collisions → more force → higher pressure
Fewer collisions → less force → lower pressure

This explains why pressure changes with temperature, volume, and amount of gas.

Factors Affecting Gas Pressure

1. Temperature

Temperature affects the speed of gas particles.

• When temperature increases → particles move faster → more collisions → higher pressure
• When temperature decreases → particles slow down → fewer collisions → lower pressure

Examples:

• A balloon expands when heated because pressure inside increases.
• A cold football becomes softer because gas pressure decreases.

2. Volume of the Container

The size of the container affects how often particles hit the walls.

• Smaller container → particles have less space → more collisions → higher pressure
• Larger container → particles have more space → fewer collisions → lower pressure

This is why compressing air in a pump increases pressure.

3. Number of Gas Particles

The more gas added to a container, the more particles there are to collide with the walls.

• More gas particles → more collisions → higher pressure
• Fewer gas particles → fewer collisions → lower pressure

This explains how inflating a tyre increases its pressure.

Practical Examples of Gas Pressure

1. Balloons and Tyres

Air molecules inside a balloon hit the walls, creating pressure that keeps the balloon inflated. When more air is added, pressure increases.

2. Pressure Cooker

Heating increases the speed of steam molecules. They collide more with the cooker walls, creating high pressure that cooks food faster.

3. Spray Cans

Gas inside spray cans is stored under high pressure. When the nozzle is pressed, gas rushes out to an area of lower pressure.

4. Breathing

When we breathe in, the volume of our lungs increases, lowering pressure inside. Air enters because outside pressure is higher.

5. Weather and Air Movement

Wind is caused by air moving from high-pressure areas to low-pressure areas.

Kinetic Theory Explanation

The kinetic theory of matter explains gas pressure very clearly:

• Gas particles move randomly and continuously.
• They collide with each other and with the walls.
• These collisions create pressure.
• Increasing temperature increases particle motion, causing pressure to rise.

This theory connects particle motion with real-life gas behavior.

Importance of Gas Pressure

Gas pressure is important for:

• Weather forecasting
• Designing tyres, balloons, and pressurized containers
• Air conditioning and refrigeration
• Blowing air into pipes and musical instruments
• Cooking in pressure cookers

Gas pressure also helps explain natural processes like wind, storms, and gas exchange in the lungs.

Conclusion

Gases exert pressure on the walls of their container because their fast-moving particles constantly collide with the walls. Each collision creates a small force, and together these forces produce pressure. Temperature, volume, and the number of particles affect how often and how strongly these collisions occur. This simple idea explains the behavior of gases in everyday life and many scientific applications.