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| Kinetic energy | the energy of a body or a system with respect to the motion of the body or of the particles in the system. |
| Kinetic theory | A theory concerning the thermodynamic behavior of matter, especially the relationships among pressure, volume, and temperature in gases. It is based on the dependence of temperature on the kinetic energy of the rapidly moving particles of a substance. |
| Gas pressure | the pressure exerted by a gas |
| Vacuum | a space entirely devoid of matter. |
| Atmospheric pressure | the pressure exerted by air molecules in the atmosphere surrounding Earth, resulthing from collisions of air molecules with objects |
| Barometers | any instrument that measures atmospheric pressure. |
| Pascal (Pa) | the SI unit of pressure |
| Standard atmosphere | a standard unit of atmospheric pressure, having a value of 1013.2 millibars or 29.9213 in. (760 mm) of mercury. |
| Vaporization | conversion of liquid to gas or a vapor |
| Evaporation | matter or the quantity of matter evaporated or passed off in vapor |
| Vapor pressure | the pressure exerted by the molecules of a vapor, esp. that part of the total pressure exerted by vapor in a mixture of gases, as by water vapor in air. |
| Boiling point | the temperature at which the vapor pressure of a liquid is just equal to external pressure on the liquid |
| Normal boiling point | the boiling point of a liquid at a pressure of 1 atmosphere |
| Melting point | the temperature at which a substance changes from solid to a liquid; the melting point of water is 0 degrees Celcius |
| Crystal | a substance in which the atoms, ions, or molecules are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice |
| Phase diagram | a diagram showing the conditions at which a substance exists as a solid, liquid or vapor |
| Triple point | the point of a phase diagram that represents the only set of conditions at which all three phases exist in equilibrium with one another |
| Sublimation | the conversion of a solid to a gas or vapor without passing through the liquid state |
