CHEM 110 Lecture Notes - Lecture 9: Intermolecular Force, Phase Transition, Vaporization
Document Summary
Substances change from one phase of matter to another if the kinetic energy of their molecules changes sufficiently. This change affects the balance between the energy of the intermolecular attractions and the energy of the thermal motions. Thus, if a substance changes its phase, it has to exchange heat with the surroundings. Under conditions of constant pressure, the energy change equals a change in enthalpy ( h). Fusion (melting): change from solid to liquid. It requires an increase in the thermal energy of the particles to disrupt the intermolecular forces between them. The amount of energy required to melt a substance is called the enthalpy of fusion ( hfus), or sometimes the heat of fusion. The amount of heat exchanged in the phase transition is an extensive property of the substance, and it is usually given on a per-mole basis.
