# TP: Ideal Gas Law and Equations of State

### Ideal Gas Law

##### DEFINITION

An equation of state relates the molar density (or specific molar volume) of a fluid (i.e., a vapor or a liquid) to the temperature and pressure of the fluid.

The most common and simplest equation of state is the ideal gas law:

$P=\frac{nRT}{V} = \frac{RT}{v}$

##### NOTE

Interestingly, the ideal gas law can be derived from our molecular understanding of the properties T and P. This requires that we assume that gas molecules are infinitely small and interact only via collisions.

##### IMPORTANT

The ideal gas law is an approximation (!) that has only limited applicability. It is usually used for diatomic gas when (RT/P)>5 L/mol and for other gases when (RT/P) > 20 L/mol (i.e., at high specific volumes!).

##### Outcome:

Use equations of state to calculate unknown properties from measured properties