General Chemistry II Worksheet #2 Intermolecular interactions, properties of liquids and solids Dr. Brosius

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1 General hemistry II ame: Worksheet #2 Intermolecular interactions, properties of liquids and solids Dr. Brosius 1 Rank these hydrocarbons, pentadecane, pentane, octadecane 1532, 512, 1838 in terms of increasing: a. viscosity 512, 1532, 1838 b. boiling point 512, 1532, 1838 rder is the same for both for same reasons, the longer the hydrocarbon chain, the more it can tangle in itself (like spaghetti); the longer chains also have a larger surface area to allow the London interactions to be maximized thus resisting flow and boiling. 2. lassify the following solids as molecular, network (covalent), metallic, ionic or atomic. a. (frozen) benzene, molecular b. diamond network covalent c. (frozen) krypton atomic d. cadmium metal metallic e. copper(ii) chloride ionic

2 3. a. Identify the dominate intermolecular force of each pure compound. 22 valence e 24 total e 32 polar 4I valence e 40 total e 96 dipole-dipole 4 + I ion-ion

3 ()2(S) valence e 26 total e 42 S S S polar ()3 valence e 26 total e 34 -bonding -bonding

4 Ar valence e 8 total e 18 London b. List the compounds in order of increasing melting point. Indicate a reason for the ordering within a group with the same intermolecular force. Ar < 22 < ()2(S) < ()3 < 4I Ion-ion, strongest, London weakest. or the two polar molecules that can ydrogen bond, the melting point has to do with many things such as: polarity (electronegativity differences) and # of -bonds the compound can form. Polarity and number of -bonds (3 versus 2) would probably make ()3 the strongest.

5 4. Given the following heating curve for ethanol (below), label/do the following: I. melting II. boiling III. heating the liquid IV. circle the specific heat capacity for the liquid V. Label the x-axis eating the liquid boiling melting eat (in J or cal) 5. or the two-dimensional array shown below, draw unit cells, that when repeated, generate the entire two-dimensional lattice. ould make a unit cell that doesn t have 90 o angles, but these are better (higher symmetry). 6. ow many whole atoms are in a primitive cubic unit cell? (A sketch may be helpful). sc (8 atoms in corner)(1/8 atom) = 1 atom 7. ow many whole atoms are in a body-centered cubic unit cell? (A sketch may be helpful). bcc (8 atoms in corner)(1/8 atom) = 1 atom + (1 atom in center of cell (filled in red) = 1 atom 2 whole atoms

6 8. a. ow many whole atoms are in a face-centered cubic unit cell? (A sketch may be helpful). fcc (8 atoms in corner)(1/8 atom) = 1 atom + (1/2 atom on face of cell (filled in red))(6 faces) = 3 atom 4 whole atoms b. Palladium is named after the asteroid Pallas, both were discovered in the early 1800 s. Pallas is probably the second largest main belt asteroid in terms of volume. If the radius of palladium is nm, and it crystallizes in a fcc arrangement, what is the volume of a unit cell of palladium (in cm 3 )? (1 nm = 1x10 9 m) These are cubic unit cells, so V=a 3 rom fcc; r = a 2/4 r = (0.138 nm)(1x10 9 m)(100 cm) = 1.38x10 8 cm ( 1 nm )( 1 m ) a = 4r/ 2 = x10 8 cm V = a 3 = (3.9032x10 8 cm) 3 = 5.95x10 23 cm 3

7 11. The phase diagram for ammonia is shown below: (the phase diagram is marked to show the thought process (aka work)). a. Indicate the phase change(s) that take place when 3 is cooled from -30 o to -90 o at a constant pressure of 1 atmosphere. gas liquid solid b. Indicate the phase change(s) that take place when the pressure on 3 is decreased from 900 to 10 torr at a constant temperature of -75 o. solid liquid gas c. Estimate the normal boiling point of 3. about 35 o d. Estimate the triple point temperature and pressure of 3. about 78 o, 40 torr