1.1.3The Particulate Nature of Matter
Pressure and Temperature in Gases — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 2 of 13 Unit quiz
Part 1 of 5Everyday observations
Hot air balloon
- Hot air balloon When the air inside a balloon is heated it expands and the balloon gets bigger.
- The gas becomes less dense as its volume increases, so the balloon rises.
Bicycle pump
- Bicycle pump Pushing in the handle reduces the volume of the air in the pump, so its pressure increases.
- The high pressure forces air into the tyre.
Over-pressurised containers
- Over-pressurised containers If the pressure inside a sealed container becomes too high, the container can leak or burst.
Part 2 of 5Gas particles and pressure (Extended)
1
Gas particles are in constant, random motion, moving quickly in all directions.
2
They collide with each other and with the inside walls of their container.
3
Each collision with a wall exerts a tiny force on it.
4
The huge number of collisions every second adds up to a steady force on the wall, which we measure as the gas pressure.
5
More frequent or harder collisions on the same area mean a higher pressure.
Part 3 of 5Effect of temperature on volume (Extended)
1Heat the gas
- Heat the gas Thermal energy is transferred to the particles, increasing their kinetic energy.
2Faster particles
- Faster particles The particles move faster and spread further apart.
3More forceful collisions
- More forceful collisions They hit the walls more often and with more force.
4Volume increases
- Volume increases If the container is flexible, the walls are pushed outwards and the volume grows, as with a balloon.
Part 4 of 5Effect of pressure on volume (Extended)
Fixed mass of gas at constant temperature
Pressure up
- Pressure up The same number of particles is squeezed into a smaller volume, so they are closer together.
More collisions
- More collisions With less space to travel, the particles hit the walls more frequently, which is what the higher pressure means.
Pressure down
- Pressure down The same particles occupy a larger volume, collisions with the walls become less frequent, and the pressure falls.
Part 5 of 5Summary
| Change | Effect on volume (or pressure) | Reason |
|---|---|---|
| Temperature increases | Volume increases if the container can expand | Particles move faster and push the walls outwards |
| Temperature decreases | Volume decreases | Particles slow down and collide less forcefully |
| Volume decreases | Pressure increases | More frequent collisions with the walls |
| Volume increases | Pressure decreases | Less frequent collisions with the walls |
Key terms
| Term | Meaning |
|---|---|
| Pressure | The force exerted by particles colliding with a surface, per unit area of that surface. |
| Kinetic energy | The energy a particle has because it is moving. |
| Random motion | Movement in constantly changing directions without any pattern. |
| Density | The mass of a substance in a given volume; it falls as a gas expands. |
| Collision | When a particle hits another particle or the wall of the container. |
Avoid these mistakes
1
Saying particles expand when heated. Particles spread out; the material expands.
2
Writing that particles are heated, rather than that they gain kinetic energy and move faster.
3
Mixing up the directiondecreasing the volume increases the pressure, not decreases it.
4
Forgetting to mention collisions with the container walls when explaining gas pressure.
Last updated: