Worksheet 8 Intermolecular Forces Key

1 Worksheet #8 Intermolecular Forces Chem 102 1. Determine the kinds of intermolecular forces ( dispersion, dipole-dipole, H-bonding) that are present in each of the following elements or compounds. a. Kr dispersion b. NCl 3 dispersion, dipole-dipole c. SiH 4 dispersion d. HF dispersion, dipole-dipole, H-bonding e. N 2 dispersion f. NH 3 dispersion, dipole-dipole, H-bonding g. CO dispersion, dipole-dipole h. CCl 4 dispersion, 2. Arrange the following compounds in order of increasing boiling point, explain your reasoning. CH 4 CH 3 CH 2 Cl CH 3 CH 3 CH 3 CH 2 OH CH 4 < CH 3 CH 3 < CH 3 CH 2 Cl < CH 3 CH 2 OH 3. Which one of the molecules would require the most energy to break the IMFs? How would you rank them in term of their boiling point? I. H 2 O II. H 2 Te III. HCl IV. HI 4. Which one of the following compounds is more likely to be a liquid at room temperature, and why? 5. The surface tension and viscosity values for diethyl ether, acetone, ethanol and ethylene glycol are shown here: a. Explain the differences in viscosity in terms of the size and shape of the molecules and their IMFs. b. Explain their differences in surface tension in terms of the size and shape of the molecules and their IMFs. H H C O C H H F H H O O H dispersion dispersion dispersion+ dispersion + (but heavier dipole-dipole dipole-dipole+ than CH 4 ) H-bonding While all three compounds have similar molar mass, and all have dispersion and dipole-dipole forces, only hydrogen peroxide has H-bonding, thus likely to have the highest b.p. amongst the three compounds. Similar trend is observed for surface tension, where the molecule with the most IMFS (ethylene glycol) will exhibit the highest surface tension. The molecules with the most IMFs will have the highest viscosity. Ethylene glycol is the largest molecule and has two H-bonding sites, whereas ethanol is small and has one -H-bonding. Diethylether is the least viscous since it does not have H-bonding