Individual & Universal Gas Constants: Definitions, Values, and Applications

Overview

Engineering reference data for Individual Universal Gas Constant in gases and compressed air.

Key Formulas

Ideal Gas Law

$PV = nRT$

Pressure × Volume = moles × gas constant × temperature.

Boyle's Law

$P_1 V_1 = P_2 V_2$

At constant temperature.

Charles's Law

$\frac{V_1}{T_1} = \frac{V_2}{T_2}$

At constant pressure.

Variables

Symbol	Description	Unit
$P$	Pressure	Pa
$V$	Volume	m³
$T$	Temperature	K
$R$	Gas constant	8.314 J/(mol·K)

Individual Gas Constants Table

Universal Gas Constant in Alternative Units

Unit System	Value
$R_u$ in J/(mol·K)	8.3144598
$R_u$ in kJ/(kmol·K)	8.3144598
$R_u$ in atm·L/(mol·K)	0.08206
$R_u$ in bar·L/(mol·K)	0.08314
$R_u$ in cal/(mol·K)	1.9872
$R_u$ in Btu/(lbmol·°R)	1.9872
$R_u$ in lbf·ft/(lbmol·°R)	1545.349
$R_u$ in atm·ft³/(lbmol·°R)	0.73024
$R_u$ in kPa·cm³/(mol·K)	8314.46
$R_u$ in hp·h/(lbmol·°R)	0.0007805
$R_u$ in kWh/(lbmol·°R)	0.000582

Molecular Weight of a Gas Mixture

The average molecular weight of a gas mixture is calculated from the mole fractions and molecular weights of the constituent gases:

$M_{\text{mixture}} = \sum_{i=1}^{n} x_i M_i = x_1 M_1 + x_2 M_2 + \cdots + x_n M_n$

Where:

• $x_i$ = mole fraction of gas $i$ in the mixture
• $M_i$ = molecular weight of gas $i$

Note: For dry air, the mixture molecular weight is approximately 28.965 g/mol (28.965 kg/kmol).

Interactive Charts

References

• Original Source