States of matter
Matter transitions between three classical states of matter (gas, solid, and liquid) and a fourth state of matter. Note that the enthalpy of a system is the heat content of a system at constant pressure. The process of a solid converting to a liquid is known as "melting"; liquid to a gas is "vaporization"; and gas back to a solid is "deposition." These same processes in the reverse direction are "freezing"; "condensation"; and "sublimation."
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"Phase change."
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