Wednesday, January 19th, 2011

Lecture on the 19th continued with a discussion of intermolecular forces. In some cases, such as water, a more extreme dipole-dipole interaction is observed. Since this is a special case, the term "hydrogen bonding" was coined. In this case hydrogen must be directly bonded to O, N, or F. At the end of this section I compared the relative strengths of the intermolecular forces and stressed that these effects are additive in molecules. We will come back to intermolecular forces in Chapter 13 when we study solutions, so be sure to know them.

Section 11.3 lists some other properties of liquids such as viscosity and surface tension. Each of these properties is dependent upon intermolecular forces.

Sections 11.4 and 11.5 go hand in hand with Experiment #13. When a substance changes phase from a solid to a liquid to a gas heat is required to facilitate this change. But the heat needed is not a simple linear increase. When one phase is converted to another there is a certain amount of energy required to change phase. When a solid melts becoming a liquid, this energy is referred to as heat of fusion and heat of vaporization is the heat required to convert a liquid to a vapor.

Exp #13 compares the heat of vaporization for alcohols and alkanes and relates them back to intermolecular forces. The Clausius-Clapeyron equation graphically shows the relationship between vapor pressure, temperature, and the heat of vaporization.