Charles's Law and Absolute Zero

Charles's Law

• Discovered by Jacques Charles (1787).
• Describes the linear relationship between the volume of an enclosed gas and its temperature when pressure is held constant.
• States that the volume of a gas is directly proportional to its absolute temperature at constant pressure ($P$) and amount of gas ($n$).
  • $V ext{ extalpha } T$ (at constant $P$ and $n$)
  • ${V ext{/ } T} = ext{constant}$ (at constant $P$ and $n$)
  • ${V<em>1 ext{/ } T</em>1} = {V<em>2 ext{/ } T</em>2}$ (at constant $P$ and $n$)
• Key Requirement: Temperature must always be expressed on an absolute scale (Kelvin). Convert Celsius to Kelvin before calculations.

Absolute Zero

• Extrapolation of gas volume vs. temperature graphs indicates that the volume of all gases approaches $0 ext{ cm}^3$ at $-273.15^{ ext{o}} ext{C}$.
• This temperature, $-273.15^{ ext{o}} ext{C}$, is defined as $0 ext{ K}$ on the Kelvin scale and is called absolute zero.
• It represents the coldest possible temperature, as a negative volume or zero volume for actual gas molecules is physically impossible.