Real Gases: Interactions, Virial EOS, and Van der Waals EOS

Vocabulary flashcards covering key concepts from real gas behavior, including intermolecular potentials, critical phenomena, compressibility, virial corrections, Boyle temperature, and the van der Waals equation.

Lennard-Jones potential

A model of intermolecular forces with short-range repulsion and long-range attraction used to describe non-ideal gas behavior and molecular interactions.

Critical point

The end point of the liquid–gas phase boundary where the phases become indistinguishable; defined by Tc, Pc, and Vc.

Critical temperature (Tc)

The temperature at the critical point above which a gas cannot be liquefied by pressure alone.

Critical pressure (Pc)

The pressure at the critical point corresponding to the critical temperature and volume.

Critical volume (Vc)

The molar volume at the critical point where liquid and gas phases cease to be distinct.

Supercritical fluid

A state of matter above Tc and Pc where the substance exhibits properties of both liquids and gases and has no distinct phase boundary.

Compressibility factor (Z)

Z = P Vm / (R T); Z = 1 for an ideal gas; deviations from 1 indicate non-ideal gas behavior.

Molar volume (Vm)

Volume per mole of substance; used in equations of state to relate P, V, and T.

Virial equation of state

An equation of state written as Z = 1 + B(T)/Vm + C(T)/Vm^2 + …, where B and C are temperature-dependent virial coefficients.

Second virial coefficient (B)

Temperature-dependent coefficient in the virial expansion that accounts for pairwise intermolecular interactions.

Third virial coefficient (C)

Temperature-dependent coefficient in the virial expansion related to three-body interactions (appears with 1/Vm^2).

Boyle temperature (Tb)

The temperature at which B(Tb) = 0; at low pressures the gas behaves ideally (Z ≈ 1) near this temperature.

Volume exclusion (b)

Finite molecular size effect; the excluded volume reduces the available space for molecular motion (in van der Waals EOS Vm is effectively reduced by b).

Van der Waals equation

An equation of state that accounts for non-ideality: (P + a/Vm^2)(Vm - b) = RT, where a accounts for attractions and b for finite molecular size.