(d) Ideal gas molecules

Explain how molecules in a gas have random motion and that they exert a force, and hence a pressure, on the walls of a container

Understand why there is an absolute zero of temperature, which is –273 °C

Describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

Understand why an increase in temperature results in an increase in the average speed of gas molecules

Know that the Kelvin temperature of a gas is proportional to the average kinetic energy of its molecules

Explain, for a fixed amount of gas, the qualitative relationship between:

• pressure and volume at constant temperature
• pressure and Kelvin temperature at constant volume

Use p₁/T₁ = p₂/T₂ for the pressure and kelvin temperature of a fixed mass of gas at constant volume.

Use p₁V₁ = p₂V₂ for the pressure and volume of a fixed mass of gas at constant temperature.