13.1 The Nature of Gases

• Particles in a gas are considered to be small, hard spheres with an insignificant volume. The motion of the particles in a gas is rapid, constant, and random. All collisions between particles in a gas are perfectly elastic.
• Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.
• The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.

13.2 The Nature of Liquids

• The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.
• During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface.
• In a system at constant vapor pressure, a dynamic equilibrium exists between the vapor and the liquid. The rates of evaporation and condensation are equal.
• At a temperature at which particles throughout a liquid have enough kinetic energy to vaporize, the liquid begins to boil.

13.3 The Nature of Solids

• The general properties of solids and the shapes of crystals reflect the orderly arrangement and the fixed locations of particles within the solids.

13.4 Changes of State

• Sublimation occurs in solids that have vapor pressures that exceed atmospheric pressure at or near room temperature.
• Conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the two regions representing the phases.