## Kelvin and Celsius Scales

Scientists commonly use two temperature scales - the Kelvin and Celsius scales. These temperature scales are closely related. The Celsius scale has been in use longer, and is based on the properties of water.
{jatex options:inline}0^{\circ} \: Celsius{/jatex}  is defined to be the freezing point of water at standard pressure  {jatex options:inline}p_0=1.1325 \times 10^5 N/m^2{/jatex}
{jatex options:inline}100^{\circ} \: Celsius{/jatex}  is defined to be the boiling point of water at standard pressure  {jatex options:inline}p_0=1.1325 \times 10^5 N/m^2{/jatex}
The Kelvin scale is more fundamental. An increase of  {jatex options:inline}1^{\circ} Celsius{/jatex}  is the same increase as an increase of  {jatex options:inline}1^{\circ} Kelvin{/jatex}, but the zero of the Kelvin scale is defined as the temperature at which no more energy can be extracted from a system, and is equal to  {jatex options:inline}-273.16^{\circ} Celsius{/jatex}.
When doing calculations, typically we use the Kelvin scale eg when using the ideal gas equation of state  {jatex options:inline}1 pV=nRT{/jatex}.