Kinetic Molecular Theory

Flashcards reviewing the kinetic-molecular theory of matter, gases, liquids, solids, and changes of state.

Kinetic-Molecular Theory

Based on the idea that particles of matter are always in motion.

Ideal Gas

A hypothetical gas that perfectly fits all the assumptions of the kinetic-molecular theory.

First Assumption of Kinetic-Molecular Theory of Gases

Gases consist of large numbers of tiny particles that are far apart relative to their size.

Second Assumption of Kinetic-Molecular Theory of Gases

Collisions between gas particles and between particles and container walls are elastic collisions.

Third Assumption of Kinetic-Molecular Theory of Gases

Gas particles are in continuous, rapid, random motion and therefore possess kinetic energy.

Fourth Assumption of Kinetic-Molecular Theory of Gases

There are no forces of attraction between gas particles.

Fifth Assumption of Kinetic-Molecular Theory of Gases

The temperature of a gas is a measure of the average kinetic energy of the particles.

Expansion (of Gases)

Gases do not have a definite shape or a definite volume; they completely fill any container in which they are enclosed.

Fluidity (of Gases)

Because the attractive forces between gas particles are insignificant, gas particles glide easily past one another.

Low Density (of Gases)

The density of a gaseous substance at atmospheric pressure is about 1/1000 the density of the same substance in the liquid or solid state.

Compressibility (of Gases)

During compression, the gas particles, which are initially very far apart, are crowded closer together.

Diffusion

Spontaneous mixing of the particles of two substances caused by their random motion.

Effusion

A process by which gas particles pass through a tiny opening.

Real Gas

A gas that does not behave completely according to the assumptions of the kinetic-molecular theory.

Liquid

A form of matter that has a definite volume and takes the shape of its container.

Intermolecular Forces (IMF)

Attractive forces between particles in a liquid.

London Dispersion Forces

Weak forces that result from temporary shifts in the density of electrons in electron clouds, present between non-polar molecules.

Dipole-Dipole Forces

Attractions between oppositely charged regions of polar molecules.

Hydrogen Bonds

Occur between molecules containing a hydrogen atom bonded to a small, highly electronegative atom (N, O, F) with at least one lone electron pair.

Fluid

A substance that can flow and therefore take the shape of its container.

Surface Tension

A force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size.

Capillary Action

The attraction of the surface of a liquid to the surface of a solid.

Vaporization

The process by which a liquid or solid changes to a gas.

Evaporation

The process by which particles escape from the surface of a nonboiling liquid and enter the gas state.

Boiling

The change of a liquid to bubbles of vapor that appear throughout the liquid.

Freezing (or Solidification)

The physical change of a liquid to a solid by removal of energy as heat.

Crystal

Substance in which the particles are arranged in an orderly, geometric, repeating pattern.

Amorphous Solid

Solid in which the particles are arranged randomly

Melting

The physical change of a solid to a liquid by the addition of energy as heat.

Crystal Structure

The total three-dimensional arrangement of particles of a crystal.

Unit Cell

The smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire lattice.

Phase

Any part of a system that has uniform composition and properties.

Condensation

The process by which a gas changes to a liquid.

Vapor

A gas in contact with its liquid or solid phase.

Equilibrium

A dynamic condition in which two opposing changes occur at equal rates in a closed system.

Equilibrium Vapor Pressure

Pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature.

Volatile Liquids

Liquids that evaporate readily; they have relatively weak forces of attraction between their particles.

Nonvolatile Liquids

Liquids that do not evaporate readily; they have relatively strong attractive forces between their particles.

Boiling Point

The temperature at which the equilibrium vapor pressure of the liquid equals the atmospheric pressure.

Normal Boiling Point

The boiling point at normal atmospheric pressure (1 atm, 760 torr, or 101.3 kPa).

Molar Enthalpy of Vaporization

The amount of energy as heat that is needed to vaporize one mole of liquid at the liquid’s boiling point at constant pressure.

Molar Enthalpy of Fusion

The amount of energy as heat required to melt one mole of solid at the solid’s melting point.

Sublimation

The change of state from a solid directly to a gas.

Deposition

The change of state from a gas directly to a solid.

Phase Diagram

A graph of pressure versus temperature that shows the conditions under which the phases of a substance exist.

Triple Point

Indicates the temperature and pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium.

Critical Point

Indicates the critical temperature and critical pressure.

Critical Temperature

The temperature above which the substance cannot exist in the liquid state.

Critical Pressure

The lowest pressure at which the substance can exist as a liquid at the critical temperature.