CHEM 102—General Chemistry
Exam #2
21 February 2003
Name _________________________
Thermodynamic Information
Hof (kJ mol-1)
-74.81
-238.66
-277.69
-110.53
249.17
-241.82
compound
CH4(g)
CH3OH(l)
C2H5OH(l)
CO(g)
O(g)
H2O(g)
compound
H2O(l)
Mn(NO3)2(s)
(NH4)2Cr2O7(s)
Cr2O72-(aq)
Cr2O3(s)
Hof(kJ mol-1)
-285.83
-576.26
-1806.7
-1490.3
-1139.7
1. (20 points) Identify the products in the condensation reaction between alanine and cysteine.
alanine:
H
O
cysteine:
H
N–C–C–O–H
N–C–C–O–H
H
CH3
O
H
CH2SH
2. (10 points) How many monomer units are in a strand of Teflon (polytetrafluoroethylene) that
has a molar mass of 138100 g mol-1?
3. (10 points) The gas within a piston is compressed from 3.00 L to 0.50 L under a pressure of
10.0 atm. If the piston is insulated from its surroundings, so no heat is exchanged, will the
temperature of the gas inside the piston increase or decrease?
4. (20 points) Ethylene (C2H4) polymerizes via a free radical mechanism, initiated by an RO
species, to form polyethylene. Draw the mechanism for the propagation step of the
reaction using line structures to represent the molecules.
5. (10 points) Which of the following are state variables?
distance
temperature
mass
area
volume
6. (10 points) Which is greater: the change in energy or the change in enthalpy when 5.00 mol
of iso-propanol (iso-C3H7OH) boil?
Hovap(iso-C3H7OH) = 42.11 kJ mol-1
7. (20 points) Determine the final temperature of the system when a 147.3 g piece of silver at
132.9 oC is placed in 1.093 L H2O(l) at 25.0 oC.
Cp(Ag) = 25.351 J mol-1K-1
Cp(H2O) = 75.291 J mol-1K-1
8. (20 points) Ammonium dichromate, (NH4)2Cr2O7(s), decomposes to form chromium(III)
oxide, molecular nitrogen, and water vapor. Is the decomposition reaction endothermic or
exothermic?
9. (10 points) Which of the following reactions represent enthalpies of formation?
2 C(graphite) + O2(g) + 3 H2(g) C2H5OH(l)
C(graphite) + O(g) CO(g)
CH4(g) + H2O(l) CH3OH(l) + H2(g)
Mn(s) + N2(g) + 3 O2(g) Mn(NO3)2(s)
10. (20 points) How many grams of methanol, CH3OH(l), must be evaporated in order to cool a
100.0 g piece of iron by 25 oC?
Hovap(CH3OH) = 39.23 kJ mol-1
Cp(Fe) = 25.10 J mol-1K-1