# What does the R stand for in the ideal gas law (PV=nRT)?

May 25, 2014

The units of the universal gas constant $R$ is derived from equation $P V = n R T$. It stands for Regnault.

If

• the pressure $P$ is in atmospheres (atm),
• the volume $V$ is in liters (L),
• the moles $n$ is in moles (mol),
• and temperature $T$ is in Kelvin (K),

then $R$ is in $\text{L"cdot"atm/mol"cdot"K}$. $R$ has the value $\text{0.082057 L"cdot"atm/mol"cdot"K}$ with the above units for the remaining variables.

In other scenarios with pressures of $\text{bars}$ instead, you may also use $\text{0.083145 L"cdot"bar/mol"cdot"K}$. However, temperature must always be in Kelvin (K), as $R$ uses units of $\text{K}$.

There is a variation of the ideal gas law that uses the density of the gas with the equation

$P M = D R T$

where $M$ is the molar mass in $\text{g/mol}$ and $D$ is the density of the gas in $\text{g/L}$.

Lastly, this video may help introduce you to the ideal gas law.