100 Points
CHEMISTRY 1A
Exam 5
Name___________________________
SHOW ALL OF YOUR WORK!
1. Draw an appropriate Lewis structure for CO22- and for CO32-.
a. Give the bond order for the C-O bond in each ion.
b. Which has the weakest bonds?
c. Which has the shortest bonds?
(6)
(2)
(2)
(2)
2. Draw the structure with no double bonds and calculate the formal charge and oxidation number for
each atom.
(8)
IO2Cl2 (I is the central atom)
3. Draw a 3-D diagram for each molecule and indicate if the molecule is polar or non-polar.
a. SiF4
b. OF2
(6)
4. Determine the molecular shape for each. Give the VSEPR class, draw the 3-D structure, and
provide an appropriate VSEPR name for the shape.
(20)
a.
IF4b.
SeO2
c.
XeF3+
d.
SCl4
5. Calculate the enthalpy of reaction using bond energies. Use the table of average bond energies
provided.
(8)
H
H
H
C
C
H
H
O
Single Bond Energies (kJ/mole)
1A
4A
5A
6A
H
C
N
O
H
436
413
391 436
C
346
305
358
N
163
201
O
146
H + OF 2
H
H
O
C
C
O
H + 2HF
H
7A
F
565
485
283
190
Multiple Bond Energies (kJ/mole)
C=C 602
CC 835
C=N 615
CN 887
C=O 732
CO 1072
6. At 432C, KP = 6.7103 for the reaction: 2 NH3(g)
NH3(g)
Calculate KP for the reaction:
3 H2(g) + N2(g)
(6)
3/2 H2(g) + 1/2 N2(g)
7. At 1050 K, KC = 1.25. The system is analyzed and these concentrations are found: [O2] = 2.45 M,
[NO] = 3.15 M, [NO2] = 1.95 M.
2 NO(g) + O2(g)
2 NO2(g)
a. Is the system in equilibrium? SHOW YOUR WORK!
(5)
b. If "No" above, which way does the system shift to reach equilibrium, and why?
(5)
8. At 312C, KP = 12.2 for the reaction:
PCl5(g)
PCl3(g) + Cl2(g)
If 0.075 mole of reactant is placed in a 5.0 L flask and heated to 312C, what is the equilibrium pressure
for each gas?
(10)
9. An experiment shows that at 15C and a total pressure of 16.0 atm., the equilibrium ratio of Z to T, in
moles, is exactly 5 to 3 respectively. Calculate KP and KC for the reaction.
(10)
9 Z(g)
4 T(g)
10. At a certain temperature, 7.68 atm. of O2(g) is placed in a 20.0 liter container with 15.24 atm. of
NH3(g) and allowed to come to equilibrium. The pressure of N2(g) is then 2.28 atm. Calculate KP for this
reaction.
(10)
3 O2(g) + 4 NH3(g)
6 H2O(g) + 2 N2(g)