Particle motion in gases (AQA GCSE Physics): Revision Notes
Particle motion in gases
What causes gas pressure?
Gas pressure happens because of moving particles. The tiny particles in a gas are always moving around. They bump into the walls of their container from all different directions.
Each time a particle hits the wall, it pushes against it. When millions of particles hit the walls every second, this creates pressure. The pressure pushes outward on all the walls equally.
Key point: Gas pressure = particles hitting container walls
How temperature affects pressure
When you heat up a gas in a sealed container, the pressure goes up. This happens in five clear steps:
- More energy - The gas particles get more kinetic energy (movement energy)
- Faster movement - The particles move around much faster
- More collisions - Fast particles hit the walls more often each second
- Stronger force - Each collision pushes harder on the same wall area
- Higher pressure - The gas pressure increases
Example: Spray Can Under Heat
Think of a spray can getting hot - the pressure inside goes up because the particles are moving faster. This is why spray cans have warnings about not leaving them in hot cars or near heat sources.
How temperature affects volume
When gas particles get hotter, they also take up more space. Here's what happens in a balloon:
- Cold gas: Particles move slowly and stay closer together
- Hot gas: Particles move faster and spread out more
Example: Heating a Balloon
If you heat a balloon, it gets bigger because:
- The particles have more energy
- They hit the balloon walls more often and harder
- The balloon stretches outward
- The volume increases
Remember: More heat = faster particles = bigger volume (if the container can stretch)
Random particle movement
Gas particles move in a random way. This means:
- You cannot predict where any single particle will go
- Particles travel in all different directions
- They move at different speeds
- Their movement cannot be worked out exactly
This random movement is why gas spreads out evenly in a container. The particles bounce around until they fill all the available space.
The randomness of particle movement is crucial - it's what makes gases behave predictably on a large scale, even though individual particles are unpredictable.
How we explain gas pressure
Scientists use kinetic theory to explain gas pressure:
- Particles are always moving and colliding
- They hit container walls from all angles
- These collisions create forces on the walls
- The total force from all collisions creates pressure
- Pressure is the same on all walls because particles move randomly
Kinetic theory connects the invisible world of moving particles to the measurable properties of gases that we can observe and measure.
Remember!
Key Points to Remember:
- Gas pressure comes from particles hitting container walls
- Hotter gas = faster particles = higher pressure (in sealed containers)
- Hotter gas = faster particles = bigger volume (in stretchy containers)
- Gas particles move randomly - you cannot predict their exact paths
- More collisions with walls means more pressure