Kinetic Theory and Real Gases — Vocabulary Flashcards

Vocabulary flashcards covering key concepts from the lecture notes on kinetic theory and real gases.

Maxwell distribution of speeds

Statistical distribution of molecular speeds in a gas described by Maxwell–Boltzmann statistics; depends on temperature and molecular mass.

Relative speed (v_rel)

The speed of a molecule relative to the surrounding gas; in the notes, for identical molecules v_rel is approximated as the square root of the mean speed.

Collision cross section (sigma)

The effective area around a molecule within which another molecule will collide; related to the molecule’s size or diameter.

Collision cylinder

The swept volume defined by the cross-sectional area and the distance traveled; any molecule inside this cylinder during the interval will collide.

Distance traveled

The distance a particle moves during a time interval, equal to v_rel × Δt.

Number density (η)

The number of particles per unit volume in a gas.

Mean free path (λ)

The average distance a molecule travels between successive collisions.

Collision frequency (z)

The number of collisions per unit time (units of s⁻¹); increases with density and relative speed.

Ideal gas (perfect gas)

A gas with no intermolecular forces and only kinetic energy; follows the ideal gas law under many conditions.

Lennard–Jones potential

A model for intermolecular forces with short-range repulsion and longer-range attraction, capturing how real molecules interact.

Van der Waals radius

The distance at which the interparticle potential crosses zero, marking the balance point between attractive and repulsive forces.

Equilibrium distance

The separation between two particles at which the interparticle potential energy is minimized.

Isotherm

A curve of pressure versus volume at constant temperature.

Condensation

Phase change from gas to liquid due to compression or cooling.

Critical point

The end point of the liquid–gas coexistence curve; defined by the critical temperature, pressure, and volume.

Critical temperature

Temperature above which a gas cannot be liquefied by pressure alone.

Critical pressure

Pressure at the critical point where liquid and gas phases become indistinguishable.

Critical volume

Volume at the critical point corresponding to the critical state.

Real gas deviations

Deviation from ideal-gas behavior due to intermolecular forces, especially at low temperature or high density.

Equation of state for real gas

Modified equations with correction factors to PV = nRT to account for non-ideal behavior.

Intermolecular forces: attractive vs. repulsive

Forces that attract at longer distances and repel at short distances, shaping the potential energy curve.