Phase transitions, reactions and equalizing of heat

1 21.1 Phase and state of aggregation

1.1 21.1.1 Phase

Homogeneous system, a system with properties that are uniform throughout.

■ A vessel of dry air under standard conditions. Heterogeneous system, a system with properties that may change discontinuously at boundary surfaces.

■ A vessel containing water, steam and air.

Phase, homogeneous part of a heterogeneous system.

Phase boundary, a separating interface between two phases.

■ A closed pot containing water and steam. The surface of water is a phase boundary. There is a gaseous phase (steam) and a liquid phase (water).

Phase transition, change of a substance in its intrinsic structure that affects the order of the system. This change in the order of the system causes a change of the temperature dependence of its properties.

■ If water is heated, it starts to boil when the boiling temperature is reached. An additional supply of heat does not lead to an increase of temperature, but only to further evaporation of water (...