Topic explanation

Standard explanation

Charles’s law states that for a fixed amount of gas at constant pressure, volume is directly proportional to absolute temperature.

Key points

• The amount of gas and pressure must remain constant.
• Volume is directly proportional to absolute temperature: V ∝ T.
• The ratio VT remains constant.
• For two states, V₁T₁ = V₂T₂.
• Temperature must be expressed in kelvin.
• The extrapolated V–°C graph reaches zero volume near −273 °C, the idealized absolute-zero intercept.

Labelled diagram