Gases, pressure and volume
Gas pressure
- A gas pushes on the walls of its container.
- This push, spread over the area, is the pressure.
- Pressure comes from gas particles hitting the walls.
Practice
Gas pressure is caused by:
Pressure is the force of countless particle collisions with the container walls, spread over the area.
Heating a gas
- Heating gives the particles more kinetic energy, so they move faster and hit the walls harder and more often.
- At fixed pressure: the gas expands — its volume increases.
- At fixed volume (sealed rigid container): the pressure rises.
Practice
Heating a gas in a sealed, rigid container makes the pressure:
With fixed volume, faster particles collide harder and more frequently, so the pressure rises.
Squeezing a gas
- Increase the pressure on a fixed mass of gas (same temperature) → its volume decreases.
- A smaller space means the particles hit the walls more often — which is what higher pressure means.
Practice
At constant temperature, increasing the pressure on a gas decreases its volume.
Squeezing the gas into a smaller space increases how often particles hit the walls — higher pressure, smaller volume.
You've got it
Key idea
- pressure = gas particles hitting the walls
- heat at fixed pressure → bigger volume; heat at fixed volume → higher pressure
- more pressure at the same temperature → smaller volume