Fasinvaihtoa

Fasinvaihtoa refers to the process of phase change, the transformation of a substance between its solid, liquid and gaseous phases as energy is exchanged with its surroundings. The process is driven by changes in temperature and pressure and is governed by thermodynamics.

Common phase transitions include melting (solid to liquid), freezing (liquid to solid), vaporization (liquid to gas), condensation (gas to liquid), sublimation (solid to gas) and deposition (gas to solid). Each transition has characteristic conditions and latent heat: energy absorbed or released during the transition without a change in temperature of the substance at the phase boundary. The phase of a substance is often represented on a phase diagram, showing stability regions for solid, liquid and gas as functions of temperature and pressure, with features such as the melting point, boiling point, triple point, and critical point.

Kinetics matter: real systems may experience supercooling or superheating, nucleation barriers, and hysteresis, causing transitions to occur at different conditions than equilibrium predictions. Practical applications include phase change materials for thermal energy storage, refrigeration and air conditioning, metallurgy, and climate phenomena.

Measurement and analysis tools include calorimetry, especially differential scanning calorimetry (DSC), which measures heat flows associated with phase transitions, and thermodynamic modeling using equations such as the Clapeyron or Clausius–Clapeyron relations.