Phase Equilibrium

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Enthalpy of Vaporization and Condensation

Definition

The enthalpy of vaporization is the amount of heat that must be absorbed to keep the liquid at a constant temperature when a given quantity is vaporized

Conversely, the enthalpy of condensation is the amount of heat that must be released to keep the liquid at a constant temperature when a given quantity is condensed

Equation

Note that , not

Enthalpies of Vaporization at 298K

Liquid Intermolecular Forces
Diethyl ether, LDF
Methyl alcohol, LDF + H-bond
Ethyl alcohol, LDF + H-bond
Water, 4 H-bonds

Trend: as intermolecular forces increase, so does the change in enthalpy

Phase Equilibrium

Definition

During phase equilibrium there is no net conversion from one phase to another. That is, speed of conversions between the two states is the same.

The pressure of water vapour at equilibrium is its vapour pressure