# Applied Mathematics/The State Equation

## Ideal gas law

As an experimental rule, about gas, the equation below is found.

${\displaystyle PV=nRT}$...(1)

where

${\displaystyle \ p}$ = Pressure (absolute)
${\displaystyle \ V}$ = Volume
${\displaystyle \ n}$ = Number of moles of a substance
${\displaystyle \ T}$ = Absolute temperature
${\displaystyle \ R}$ = Gas constant
${\displaystyle R\simeq 8.31J(Kmol)^{-1}}$

The gas which strictly follows the law (1) is called ideal gas. (1) is called ideal gas law. Ideal gas law is the state equation of gas. In high school, the ideal gas constant below might be used:

${\displaystyle R=0.082LatmK^{-1}mol^{-1}}$

But, in university, the gas constant below is often used:

${\displaystyle R=8.31JK^{-1}mol^{-1}}$