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.
elastic collision
Collisions in which there is no net loss of total kinetic energy.
diffusion
The spontaneous mixing of the particles of two substances caused by their random motion.
effusion
Process by which gas particles pass through any tiny opening.
real gas
A gas that does not behave completely according to the assumptions of the kinetic-molecular theory
fluid
Substance that can flow and therefore take the shape of its container.
surface tension
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 a solid changes to a gas.
evaporation
The process by which particles escape from the surface of a nonboiling liquid and enter the gas state.
freezing
The physical change of a liquid to a solid by removal of energy as heat.
crystalline solids
Solids that consist of crystals.
crystal
A substance in which the particles are arranged in an orderly, geometric, repeating pattern.
amorphous solids
A 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.
melting point
The temperature at which a solid becomes a liquid.
supercooled liquids
Substances that retain certain properties even at temperatures at which they appear to be solid.
crystal structure
The total 3D arrangement of particles of a crystal.
unit cell
The smallest portion of a crystal lattice that shows the 3D pattern of the entire lattice.
lattice
The arrangement of particles in the crystal can be represented by a coordinate system.
phase
Any part of a system that has uniform composition and properties.
condensation
The process by which a gas changes to a liquid.
equilibrium
A dynamic condition in which two opposing changes occur at equal rates in a closed system.
equilibrium vapor pressure
The pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature.
volatile liquids
Liquids that evaporate readily.
boiling
The conversion of a liquid to a vapor within the liquid as well as on its surface.
boiling point
The temperature at which the equilibrium vapor pressure of the liquid equals the atmospheric pressure.
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.
freezing point
The temperature at which the solid and liquid are in equilibrium at 1 atm 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 the 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.