vesifaasi

Vesifaasi is a term used in Estonian-language science to refer to the phase state of water and the transitions between its phases. It encompasses the three classical phases of water: ice (solid), liquid water, and water vapor (gas), as well as the conditions under which each phase is stable.

The relationships among the water phases are summarized in the water phase diagram, which maps temperature and pressure to stability regions for ice, liquid water, and water vapor. At standard atmospheric pressure, ice melts at 0°C and liquid water boils at 100°C; the triple point, where ice, liquid water, and water vapor coexist, occurs at about 0.01°C and 611.657 pascals. The critical point for water lies at about 647.1 kelvin and 22.064 megapascals, beyond which liquid and gaseous phases are indistinguishable.

Water’s phase behavior is influenced by its unique properties, including a density maximum near 4°C and extensive hydrogen bonding. These characteristics lead to phenomena such as ice being less dense than liquid water and the existence of several high-pressure ice forms (for example, ice VI and ice VII). Understanding vesifaasi is important across meteorology, climatology, hydrology, geology, and chemical engineering, where phase changes affect processes like freezing and melting, condensation and evaporation, and the use of water under extreme conditions.

Methods for studying phase transitions include calorimetry and differential scanning calorimetry, as well as spectroscopic techniques and high-pressure experiments. In practical applications, vesifaasi informs the modeling of weather and climate, the design of industrial processes, and analyses of environments and planetary systems where water phase changes govern dynamics. See also phase diagram, phase transition, water.