Particle Model & Pressure (AQA GCSE Physics Combined Science): Revision Notes
Particle motion in gases
Gas pressure happens because tiny particles are constantly moving and hitting the walls of their container. Understanding how these particles behave helps explain many important gas properties.
How gas pressure works
Gas particles are always moving around randomly inside a container. When they bump into the walls, they create pressure. Here's what happens:
- Gas particles move in all directions
- They hit the container walls at different angles
- Each collision creates a small push on the wall
- All these pushes together create gas pressure
- The pressure acts at right angles to the wall surface
Think of it like bouncing balls in a box - the more they hit the sides, the more force you feel. This simple analogy helps visualise how millions of invisible gas particles create the pressure we can measure.
What affects gas pressure
You can increase gas pressure in three main ways:
Increasing temperature
- Hotter particles have more energy
- They move faster and hit walls harder
- More collisions happen each second
- This creates higher pressure
Adding more gas
- More particles means more collisions
- The same wall area gets hit more often
- Pressure increases
Making the container smaller
- Same number of particles in less space
- Particles hit the walls more frequently
- Pressure goes up
Key Factors Affecting Gas Pressure:
- Temperature increase → faster particles → higher pressure
- More particles → more collisions → higher pressure
- Smaller volume → more frequent collisions → higher pressure
Temperature and pressure relationship
When you heat a gas in a sealed container, several things happen in order:
- Gas molecules gain more kinetic energy
- Molecules move faster than before
- More collisions occur between molecules and container walls
- Greater force is applied to the same wall area
- The gas pressure increases
This explains why aerosol cans can explode if they get too hot - the pressure inside becomes dangerously high. Never leave pressurised containers in direct sunlight or near heat sources.
Temperature and volume relationship
If gas is in a flexible container (like a balloon), heating it has a different effect:
- The balloon contains a fixed amount of gas
- At constant temperature, particles move at steady speeds
- When you heat the gas, particles move faster
- Faster particles hit the balloon walls more often
- The balloon expands to give particles more space
- This keeps the pressure roughly the same
Everyday Example: Balloon Behavior
Step 1: Take a balloon outside on a cold day
- The cold air causes gas particles to move slower
- The balloon appears deflated and smaller
Step 2: Bring the same balloon into a warm room
- Warmer air makes particles move faster
- The balloon expands and appears more inflated
This demonstrates how temperature affects gas volume when pressure can adjust.
Random motion in gases
Gas particles move in a completely random way. Random motion means:
- You cannot predict where any single particle will go
- Particles travel in different directions
- They move at different speeds
- Individual particle paths cannot be determined accurately
- Only the average behaviour of all particles can be predicted
Even though we can't track individual particles, we can understand the overall effects when billions of particles move together.
Scientists use statistical methods to understand gas behaviour because dealing with individual particles is impossible. Instead, they study the collective behaviour of huge numbers of particles to make accurate predictions about gas properties.
Remember!
Key Points to Remember:
- Gas pressure comes from particles constantly hitting container walls
- Higher temperature means faster particles and higher pressure
- More gas or smaller volume both increase pressure
- Random motion means individual particles move unpredictably
- Heating gas in a flexible container makes it expand rather than increase pressure