CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 173
of the solid in the liquid. In multicomponent systems, transition from one liquid phase to
another—extraction—may also occur.
7.1.4 Boiling point
In pure substances, theboiling pointis determined by the boiling temperature and the boiling
pressure. Theboiling temperatureis a temperature at which a liquid of a given composition
is in phase equilibrium with its vapour at a chosen pressure p. Theboiling pressure is
a pressure at which a liquid of a given composition is in equilibrium with its vapour at a
chosen temperature. The boiling pressure of pure substances is called thesaturated vapour
pressure, see7.1.7. In mixtures, the boiling point is determined by the boiling temperature,
the boiling pressure and the composition of the liquid phase.
Example
The boiling temperature of water atp= 8.59 MPa is 300◦C. The boiling temperature of an
equimolar mixture of ethanol and water at 13.3 kPa is 35.9◦C.7.1.5 Normal boiling point
The normal boiling point is determined by the normal boiling temperature, normal pressure
p= 101.325 kPa and the composition of the liquid. Thenormal boiling temperatureis a
temperature at which a liquid of a given composition is in phase equilibrium with its vapour
at the normal pressure.
Example
The normal boiling temperature of ethanol is 351.44 K.7.1.6 Dew point
The dew point is determined by the temperature, pressure and composition of the vapour
phase. In a pure substance it is identical with the boiling point. Thedew temperatureis
a temperature at which a vapour of a given composition is in equilibrium with its liquid at a