Gas particles move randomly at high speed and collide with the walls of their container, exerting a force. Pressure is force per unit area. Raising the temperature of a gas at constant volume makes the particles move faster, so they hit the walls more often and harder: the pressure increases. The average kinetic energy of the particles is proportional to the absolute (kelvin) temperature.
For a fixed mass of gas at constant temperature, pressure × volume = constant (p V = constant). Halving the volume doubles the pressure, because particles hit the walls twice as often. Doing work on a gas, such as pumping up a bicycle tyre quickly, increases its internal energy, so its temperature rises.
Worked example
A gas at 100 kPa occupies 3 m³. It is compressed to 1 m³ at constant temperature. What is the new pressure?
- p₁V₁ = p₂V₂.
- 100 × 3 = p₂ × 1.
Answer:p₂ = 300 kPa.
Key words
- pressure
- force per unit area
- absolute zero
- 0 K or −273 °C, when particles have least energy
- kelvin
- temperature scale starting at absolute zero
- p V = constant
- for a fixed mass of gas at constant temperature
New questions every time.
NGSS-referenced: HS-PS3-2