CIE iGCSE Co-ordinated Sciences-P2.1.3 Pressure changes- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P2.1.3 Pressure changes – Study Notes
CIE iGCSE Co-ordinated Sciences-P2.1.3 Pressure changes – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Supplement
- Describe qualitatively, in terms of particles, the effect on the pressure of a fixed mass of gas of:
(a) a change of temperature at constant volume
(b) a change of volume at constant temperature
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Effect of Temperature and Volume on Gas Pressure
Consider: A fixed mass of gas contained in a closed container.
(a) Change of Temperature at Constant Volume
The volume of the container remains constant, so the distance between particles and walls does not change.
- Raising the temperature increases the average kinetic energy of the particles.
- Particles move faster and collide with the container walls more frequently and with greater force.
- The pressure of the gas rises because pressure is the force per unit area on the walls: \(\mathrm{P = \frac{F}{A}}\)
- Lowering the temperature slows particle motion → collisions are less frequent and weaker → pressure decreases.
Key idea: At constant volume, pressure changes are due to changes in particle speed and collision force.
(b) Change of Volume at Constant Temperature
The temperature remains constant, so the average kinetic energy of the particles does not change.
- Decreasing the volume brings walls closer together → particles collide more often with walls → pressure increases.
- Increasing the volume spreads the particles farther apart → collisions are less frequent → pressure decreases.
Key idea: At constant temperature, pressure changes are due to changes in collision frequency, not particle speed.
Conceptual Table
| Factor Changed | Effect on Particles | Effect on Pressure |
|---|---|---|
| Temperature ↑ at constant volume | Particles move faster → more energetic collisions | Pressure ↑ |
| Temperature ↓ at constant volume | Particles move slower → weaker collisions | Pressure ↓ |
| Volume ↓ at constant temperature | Particles collide more frequently with walls | Pressure ↑ |
| Volume ↑ at constant temperature | Particles collide less frequently with walls | Pressure ↓ |
Example :
A sealed container of gas is heated. Explain qualitatively why the pressure increases using the particle model.
▶️ Answer/Explanation
Heating increases particle kinetic energy → particles move faster → collide more frequently and with greater force → pressure rises.
Example :
A gas at room temperature is compressed to half its original volume without changing temperature. Explain what happens to its pressure.
▶️ Answer/Explanation
Volume decreases → particles collide more frequently with walls → pressure increases, even though particle speed (temperature) is unchanged.