Liquids and Solids

I. Intermolecular Forces
A. Forces that occur between molecules. Changes in states are due to changes in the forces among the molecules.
B. Dipole-Dipole Forces. Molecules with dipole moments can attract each other electrostatically by lining up so that the positive and negative ends are close to each other. A strong type of dipole-dipole bonding is seen in molecules that have hydrogen attached to a highly electronegative atom such as oxygen. This is called Hydrogen Bonding.
C. London Forces that exist among noble gas atoms and nonpolar molecules are relatively weak. These molecules actually have instantaneous dipoles that allow them to have intermolecular forces. London forces increase with the size of the atom.

II. Liquids
A. Surface Tension is the resistance of a liquid to an increase in its surface area.
B. Capillary action is the spontaneous rising of a liquid in a narrow tube. Cohesive forces are intermolecular forces between the molecules of the liquid. Adhesive forces are intermolecular forces between the molecules and the container.
C. Viscosity is the measure of a liquid's resistance to flow. Molecules with greater forces are more viscous.

III. Vapor Pressure and Changes of State
A. The energy required to vaporize 1 mole of a liquid at a pressure of 1 atm is called the heat of vaporization (DHvap). There is also the heat of fusion which is the energy required to melt 1 mole of a liquid. Vapor pressure is the pressure of the vapor when it is in equilibrium with the liquid. Liquids with high vapor pressures are said to be volatile. The vapor pressure depends on the intermolecular forces of the liquid.
B. Temperature increases the vapor pressure of a liquid. The equation for this increase is as follows: ln(Pvap) = -(DHvap/R)*(1/T) + C. Another important equation is as follows: ln(PvapT1/PvapT2) = (DHvap/R)*(1/T2-1/T1). This can be used to find the final temperature of a change in the vapor pressure or vice versa.
C. Sublimation is when a solid changes directly to a gas. The normal melting point is defined as the temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure is 1 atmosphere.

IV. Phase Diagrams
A. The phase diagram for water has a negative slope. The triple point is where all three states of a substance coexist. The critical temperature is where the vapor cannot be liquefied no matter what pressure is applied and the critical pressure is where this occurs.