04 Charles's Law, Absolute Zero, and the Kelvin Temperature Scale
Jacques Charles investigated the thermal expansion of gases under constant pressure:
All gases, irrespective of their chemical composition, expand by exactly the same fraction (1/273) of their volume at 0°C for every one degree Celsius temperature increase, provided the pressure remains constant: Vt = V0 (1 + t / 273).
- This universal behavior led to the discovery of Absolute Zero: If a gas is cooled continuously below 0°C, its volume decreases linearly until, at -273°C, its theoretical volume would vanish.
- Lord Kelvin established the Absolute Temperature Scale starting at -273°C (0 K):
T (Kelvin) = t (Celsius) + 273.
Expressed in Kelvin: V1 / T1 = V2 / T2 (Charles's Law).
Gay-Lussac / Pressure Law: When the volume is held strictly constant (in a rigid sealed container), the pressure of the gas increases linearly with absolute temperature: P1 / T1 = P2 / T2. The pressure coefficient of gases (βp) equals exactly 1/273 °C-1, demonstrating thermodynamic symmetry with volume expansion.