Gibbs phase rule

Water phase diagram

A dispersion system is a system containing at least two phases or two components (one – the proportion is dispersed in the other – the environment). A two-phase dispersion system is heterogeneous because there are clear boundaries between the dispersion fractions in the dispersion medium. Conversely, a system consisting of two components in one phase is homogeneous (sugar dissolved in water) and its components are not optically distinguishable.

Gibbs phase rule: f + v = s + 2

s = number of components of the system, f = number of phases of the system, v = degrees of freedom (temperature, pressure)

• The liquid and its vapor (s = 1, f = 2) have one degree of freedom - only the pressure or only the temperature can be changed.
• If we want to change both temperature and pressure, there can only be one phase.
• If phase three is to be maintained in equilibrium, it will only happen at a given temperature and pressure (v = 0) – at the so-called triple point.
  • For water, the triple point is 273.16 K (0,01 °C) at a pressure of 610.6 Pa

Links

Source

• KUBATOVA, Senta. Biofot [online]. [cit. 2011-01-31]. <https://uloz.to/!CM6zAi6z/biofot-doc>.