Chem 165 Spring08
Chem 165 Homework #1 due in class Monday April 7
1. Problem 20.3. This is an approximate calculation because of the vagueness of the “average bond
enthalpies” (which depend on the choice of compounds the assembler chooses to average).
2. Problem 20.8
3. Draw the Lewis dot structure with all of the electrons for CHCl3 (chloroform) and sketch the three-
dimensional structure. What is the hybridization of the carbon atom?
4. For the following organic compounds, draw line structures (structures with carbons just indicated as
the vertices between line segments, without the letter “C,” and hydrogens not indicated):
(i) all the linear isomers of pentene – and name each isomer
(ii) all the isomers of pentene that are branched (not a linear chain) and still are alkenes
(iii) one isomer of pentene that is an alkane.
(iv) C6H5CH=CH2 (an ethylene with one hydrogen replaced by a phenyl group, called styrene)
5. Fats are tri-esters with long hydrocarbon chains, as described in on pages 728-730. Consider the
structure drawn for a major fat component of sunflower oil shown on p. 729 (just above Figure 20.12)
which contains three C18 fatty acids, called linoleic acid.
(a) There are potentially a number of geometric isomers of linoleic acid; which one is found in
biology? (A little searching on the web or in organic chemistry books will tell you this.)
(b) When linoleic acid is “partially hydrogenated” in an industrial process (p. 730), two isomers of
the mono-alkene are formed. Which one has been in the news recently as being bad for you? (You’ll
see some products advertised as containing “none” of this.)
6. Problem 20.51 and:
addendum to question (b): Would you classify these are similar or different? Why do you think these
are different or similar?
(c) As I’m sure you know, there is a lot of interest in using biomass derived ethanol as a transportation
fuel (in the U.S., typically from corn kernels, which is very inefficient, but in Brazil they are making
it much more efficiently from sugar cane). Calculate the heat derived from combustion of a gallon of
ethanol. Ethanol has a liquid density of 0.789 g/mL and a heat of formation of –276.2 ± 2.0 kJ mol-1.
Assume that you start with liquid ethanol and make gaseous products (what would be alternative
assumptions?)
(d) Compare the heat of combustion of a gallon of ethanol to that of a gallon of iso-octane (as a model
for gasoline). Do you think you can drive a car as far on a gallon of ethanol as on a gallon of
gasoline?
(e) Nobel Laureate George Olah has written extensively about using methanol instead of ethanol, and
DuPont and BP and others are advocating for bio-derived butanol as a better fuel than ethanol.
Without calculating anything – just looking at the molecules and the products of combustion and
trying to see a pattern –can you guess what the order of energy density is for the four molecules iso-
octane, ethanol, methanol, and butanol. Energy density is the heat of combustion per gallon.
7. Look over the article “Grand Challenges and Great Opportunities in Science, Technology, and Public
Policy” in Science 2006, 314, 1696-1704. The reference format is Journal Name Publication Year,
Volume, page numbers. Science magazine publishes articles that report new scientific results,
