Non Ideal Gas Van Der Waals Equation Constants Gas Law

Overview

Engineering reference data for Non Ideal Gas Van Der Waals Equation Constants Gas Law 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)

Van der Waals Constants Table

The van der Waals constants $a$ and $b$ vary significantly between different gases, reflecting their unique intermolecular forces and molecular volumes. The following table provides these characteristic constants for a wide range of gases and vapors. The constant $a$ (in bar·L²/mol²) corrects for intermolecular attractive forces, while $b$ (in L/mol) corrects for the finite volume occupied by the gas molecules.

Unit Conversions for Van der Waals Constant $a$

The constant $a$ in the table is provided in bar·L²/mol². To use it in equations where pressure is in other units:

• To convert to atm·L²/mol²: Multiply the tabulated $a$ value by $0.986 \, \text{atm/bar}$.
• To convert to kPa·L²/mol²: Multiply the tabulated $a$ value by $100.0 \, \text{kPa/bar}$.

The constant $b$ is an inherent volume correction and does not require unit conversion for standard use in the van der Waals equation.

Physical Interpretation of the Constants

• Constant $a$: This parameter quantifies the strength of attractive forces between gas molecules. A larger $a$ indicates stronger intermolecular attraction, which reduces the pressure exerted by the gas compared to an ideal gas.
• Constant $b$: This parameter represents the effective volume occupied by one mole of the gas molecules themselves (their "excluded volume"). It is always positive and increases with the size of the molecule.

For an ideal gas, both $a$ and $b$ are zero, and the van der Waals equation simplifies to the ideal gas law: $PV = nRT$.

Interactive Charts

References

• Original Source