Honors Chemistry
Final Exam Review Sheet II
Name: ANSWERS (in red or highlighted)
1. According to the phase diagram for carbon dioxide
a. Using the kinetic molecular theory, explain why solids, liquids and gases exist in the 3 regions on the graph they
are shown to be in. Solids have molecules that have very low energy and little movement (they only vibrate about
fixed points). Most solids, except for ice, are more compact and dense than its liquid form, so solids will tend to
form at low temperatures (little molecular movement) and high pressures (condensed form). Gases are the exact
opposite and tend to favor large range of motion. Gases diffuse to occupy maximum space so they favor high
temperatures (fast particle movement) and low pressure (particles are not forced close together). Liquids have
molecular movement in between that of gases and solids so they are found on phase diagrams in the ranges of
medium pressure and medium temperature.
b. What phase changes do the lines represent? The solid + gas line represents sublimation (sg) and deposition (g
s). The solid + liquid line represents melting (sl) and freezing (ls). The liquid + gas line represents vaporization
(lg) and condensation (g l).
c. What is the triple point? The triple point is the specific temperature and pressure at which all three phases of
matter coexist at equilibrium. This means that the rate the solid is becoming gas is equal to the rate that gas becomes
solid, which is equal to the rate that gas becomes liquid which is equal to the rate at which liquid becomes solid
which is also equal to the rate that liquid becomes solid and the rate at which solid becomes liquid.
d. What phase exists at a pressure of 2 atm and a temperature of 30°C? Gas
2. How can the value of R, the gas constant, be calculated from standard data? Using the ideal gas law (PV=nRT),
the value of R can be calculated by plugging in 1.00 atm for P and 273 K for T (because standard data is at STP) and
at STP, the molar volume is 22.4 L/mol so you can use V = 22.4 L and n = 1.00 mol. Use all of these values and
solve for R (R = PV/nT)! This is a handy trick in case you can’t remember the value of R. Make sure to keep track
of the crazy label!
3. What does VSEPR stand for? What is this theory used for? VSEPR stands for valence shell electron pair
repulsion. This theory is used to predict the molecular geometries for molecules and is based on the idea that
electron clouds will repel each other within a molecule, so molecules take on specific geometries to maximize the
angles and distances between its atoms.
4. Draw the Lewis dot structures for the following:
OF2
BeCl2
NOTE: This central atom is an octet rule exception. Beryllium only has two
valence electrons available for bonding so it can only make two bonds. It doesn’t have enough orbitals to take in any
additional electrons.
H 2O 2
C2H4
CN-
I3NOTE: This central atom is an octet rule
exception. The picture must show a total of 22 electrons and the only logical place to put the extra 2 e - is on the
central atom because the iodine is capable of using its d orbitals. For the sake of symmetry, the extras go on the
central I instead of one of the outer two.
5. What are the molecular shapes for the following?
BF3 = trigonal planar
H2Te = bent
CO32-= trigonal planar
RnS3 = trigonal planar
SnCl4 = tetrahedral
CH3NH2 = tetrahedral (C), trigonal pyramidal (N)
6. Which of the following molecules are polar?
ICl = sp3
H2S = sp3
3
PF5 = sp d
SF4 =sp3d
NI3 = sp3
XeF6 = sp3d3
7. Referring back to question 6, what are the hybridizations of the central atoms? See #6
8. What is a resonance structure? Illustrate this concept with an example. A resonance structure occurs when the
bonding of a molecule cannot be accurately represented by a single Lewis structure. This happens when there is a
combination of single and multiple bonds that could be drawn in different locations and still satisfy the octet rule for
all atoms. In reality, the bonds are neither single nor multiple; they are an average somewhere in between. For
example, benzene (C6H6) has resonance.
Notice that the single and double bonds are reversed between the two pictures.
9. What is the volume of 5 moles of H2 at STP? 112 L (ignore sig figs on this one – think of the 5 moles as a
counting number that doesn’t fall under the sig fig rules).
10. You capture 8 grams of hydrogen gas in a balloon. If it is at room temperature (25C), and at room pressure
(758 mmHg), what must the volume of the balloon be? V = 97.2 L (NOTE: I’m sure Mr. Knittel really meant
8.00 g so that his final answer wouldn’t have just one measly SF  - and also, I used 2.02 g/mol for H2, so if
you used n= 4.00 mol instead of 3.96 mol like I did, you will get V = 98.1 L. Oh, and if you really want to be
die hard about the SF, then the answer will be 100 L).
11. What must the pressure be in a balloon that holds 5.1 L of gas at 20C if there are 2 moles of gas in the balloon?
Gasp! P = 9 atm with the 1 SF. With 2 SF (from the volume), the answer is 9.4 atm.
12. 5.36 liters of nitrogen gas are at -25C and 733 mm Hg. What would be the volume at 128C and 1.5atm? V2 =
5.6 L
13. At the same temperature and pressure, how much faster will nitrogen gas diffuse than chlorine gas? Nitrogen
diffuses 1.59x faster than chlorine.
14. What is the molar mass of a gas that has a mass of 40.0 grams in a volume of 2.0 L at a pressure of 1.12 atm and
a temperature of -10°C. 4.2 g/mol