Gas Pressure from the Kinetic Model

Gas pressure is caused by gas particles colliding with the walls of their container. Each collision exerts a small force on the wall. The combined effect of billions of collisions per second creates a measurable pressure.

How pressure arises

1. Gas particles move randomly in all directions at high speed.
2. They collide with the container walls.
3. Each collision causes a change in momentum, which means a force is exerted on the wall.
4. Pressure = total force from all collisions / area of wall.

Effect of temperature

Increasing temperature:

• Particles move faster (higher average kinetic energy).
• Collisions with the walls are harder (greater momentum change per collision).
• Collisions happen more frequently (particles reach the walls sooner).
• Result: pressure increases (if volume is constant).

Effect of volume (at constant temperature)

Decreasing volume:

• Particles are closer together and closer to the walls.
• Collisions with the walls happen more frequently (particles travel shorter distances between collisions).
• Result: pressure increases.

Effect of number of particles

Adding more gas particles (at constant temperature and volume):

• More collisions with the walls per second.
• Result: pressure increases.

Common errors and how to correct them

• Saying particles collide with each other to create pressure. Pressure comes from collisions with the WALLS, not between particles.
• Saying particles “slow down” at lower temperatures. They have lower average speed, but some particles still move fast.

How to apply this in an exam

Explain the mechanism: particles collide with walls, exerting force over an area. Then explain how changing temperature or volume changes the frequency or force of collisions.