# Why is the kelvin scale used for gas laws?

Dec 28, 2015

It is the most appropriate temperature scale for kinetic theory.

#### Explanation:

As you are probably aware, there are three different temperature scales that we may convert between: Celsius , Fahrenheit , and Kelvin . The degrees for these scales are based on different things.

Celsius was defined historically: this means that its degrees were set as was required for earlier scientific purposes. This is why the melting point of water at atmospheric temperature and pressure is ${0}^{\circ} \text{C}$ and its boiling point ${100}^{\circ} \text{C}$: oddly specific, but this is because this was what was required in pre-modern science and, more importantly, in daily applications. This is still true today, hence why we employ it in almost all aspects of daily life: the same is true of the Fahrenheit scale.

On the other hand, Kelvin is defined scientifically by thermodynamics. Specifically, $0 \text{K}$ is the quantity known as absolute zero, the physically coldest possible temperature that is equivalent to $- {273.15}^{\circ} \text{C}$ (Wikipedia). Since the Kelvin scale is defined by thermodynamics in this way, it is the scale most appropriate for our ideal gas laws which, by its very nature, is an area of thermodynamic investigation.

Because of how applicable it is to modern science, the Kelvin scale is actually the Système International, or SI unit for temperature.