PSI AP Chemistry: States of Matter
Practice Problems
Name _______________________
1. The melting and boiling points of ammonia are -77 C and -33 C respectively
@ standard pressure.
a. Draw a heating curve that shows the heating of solid ammonia from 100 C to 0 C showing the following:
i. Y axis labeled as temperature (K) and x axis as energy added.
ii. Label states found within each part of curve.
iii. Clearly indicate where KE is increasing and where PE is
increasing.
iv. Be sure to indicate the relative difference in energy required to
melt and vaporize the substance.
b. How many J of energy are required to heat 34 grams of ammonia from
-100 C to -50 C? The heat of fusion of ammonia is 5.63 kJ/mol.
Assume the specific heat of ammonia(s) is 4.45 J/gK as both a solid
and liquid.
c. Based on the particle interactions, would you expect it to take more or
less energy to heat carbon dioxide through this temperature range?
Justify your answer by describing the particle interactions in each
substance.
2. For each of the following, agree or disagree with the following statements
then justify your answer:
a. The melting of ice is an endothermic event.
b. Sublimation can occur above the triple point
c. Raising the pressure increases the boiling point.
d. When covalent molecular materials go through a phase change, it is
the intramolecular covalent bonds inside that are breaking.
3. For each of the following, indicate the particle interactions involved and
describe if they are forming or breaking:
a. NaCl(s)  NaCl(l)
b. Fe(l)  Fe (s)
c. CH4(g)  CH4(l)
4. Why does heating a material at a constant pressure result in a phase change?
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5. Explain why the heat of vaporization of propane (CH3CH2CH3) is 15.7 kJ/mol
while that of propanol (CH3CH2CH2OH) is 44 kJ/mol.
6. Examine the phase diagram below and answer the following questions:
a.
b.
c.
d.
e.
Which phase changes are possible at pressures below 1000 Pa?
What state cannot be found below 1000 Pa?
At what temperature will this material boil @ 105 Pa?
At what temperature will this material boil @104 Pa?
If this material were cooled from 700 K to 100 K at a constant pressure of
104 Pa, what phases changes will occur (in correct order).
7. When 36 grams of ice @ 0C were added to 100 grams of water @70 C, the ice
melted. Given that the heat of fusion of ice is 6.00 kJ/mol.
a. How much heat was absorbed from the water?
b. Assuming the specific heat capacity of water is 4.2 J/gC, by how much did
the temperature of the water decrease?
8. Br2(s) melts at -7.2 C, KBr(s) melts at 734 C and K(s) melts at 64 C.
a. Explain, in terms of types of material and particle interactions the vast
differences in melting points amongst these solids.
b. Which of the solids above would:
i. Conduct electricity after it melted but not before
ii. Has non-directional covalent bonds between atoms
9. Both methane (CH4) and diamond (C) contain the element carbon but the two
have very different melting points.
a. Which of the two would have a higher melting point and why?
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b. The substances are similar in that neither is a good conductor
compared to solid copper. Explain why methane and diamond are
poor conductors while copper is a good conductor.
10. Consider the properties of density and viscosity. Explain what happens to
the measured magnitude of these properties when the following processes
occur:
a. Iron metal freezes in a cast.
b. Liquid water is heated from 10 C to 30 C
11. For the following, agree or disagree with the statement and justify your
reasoning:
a. CuCl2(s) is an excellent conductor of electricity
b. I2(s) has a higher melting point than F2(s) because I atoms have a
greater atomic radii.
c. A solid chunk of wax (C50H102) consists of many wax molecules held
together by relatively weak intermolecular forces.
d. When KCl(s) melts, intermolecular forces are stretched.
e. Na will have a lower melting point than Mg
f. Liquids have a similar density to gases compared to solids
g. Liquids and gases have smaller viscosities than do solids
h. There are no intramolecular forces in a covalent molecular solid
12. For each of the following, determine which of the substances below is being
described:
Cu(OH)2
PH3
SiO2
W
a) Many molecules held together by intermolecular forces
b) Poor conductors in any state, high melting points
c) Brittle, high melting points, consist of charged ions held together by
Coulombic forces.
d) Malleable, delocalized electrons
e) Lowest melting point
13. Potassium chlorate (KClO3) can be decomposed at high temperatures into
potassium chloride and oxygen gas:
a. Write the balanced chemical reaction
b. If 61 grams of potassium chlorate are decomposed @ 615 torr and 12
C, and the resulting oxygen gas was collected over water; assuming
water has a partial pressure of 14.2 mm Hg @12 C ….
i. What was the pressure of dry gas collected?
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ii. How many L of oxygen gas would be theoretically collected?
iii. How many moles of water vapor must have been in the
mixture?
iv. What would have been the relative speed of oxygen gas
compared to that of the water vapor in the collection bottle?
14. Two containers of equal volumes are shown below.
a) Compare the densities of the gases. Explain your reasoning.
b) Compare the average kinetic energy of the gas molecules. Explain your
reasoning.
c) Compare the pressures of the gases. Explain your reasoning.
d) Compare the average molecular speed of the gases. Explain your
reasoning.
e) Which gas sample would behave more ideally? Explain your reasoning.
15. A toxic gas has a vapor density 4.5 x that of air which has a density of 1.225 g/L
@ 1 atm of pressure and 15 C.
a) What is the molar mass of this gas?
b) Identify the gas based on it being one of the four possibilities (CH4, C2Cl3H,
O2, CHCl3)
c) If the temperature were increased by a factor of 3 (in celsius), and the
pressure was increased by a factor of 9, what would be the new density of air
under these conditions?
16. A mixture of gases includes equimolar amounts of neon, argon, and krypton at
10 C and a total pressure of 745 torr. How many grams of argon would be present if
the container had a volume of 18.4 L?
17. Agree or disagree with the following statements, providing justification for your
choices:
a) All He atoms would be moving at the same speed at a given temperature?
b) Carbon dioxide will move approximately twice as slow as neon gas
because it has twice the mass.
c) Real gases have higher measured pressures than do ideal gases.
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d) Gases behave most real at low temperatures and low pressures
e) Water vapor will behave less ideal than H2 gas @STP
f) The density of a gas and the temperature of a gas are directly related.
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1.
2.
3.
Answer Key
a.
b.
3480 J + 11260 J + 4085 J = 18825 J
c.
Less energy, CO2 being non-polar only has weak LDF’s relative to
ammonia’s LDF’s and H-bonding.
a. Agreed, bonds must be stretched to melt and this requires energy.
b. Disagree, the solid and gas phases are never in equilibrium at
pressures above the triple point pressure.
c. Agree, raising the atmospheric pressure means the temperature
must be raised further for the molecules to weaken the Coulombic
forces between them.
d. Disagree, it is the weak inter-molecular forces that are weakening
when covalent molecular materials experience a phase change.
a. Intramolecular, ionic, weakening.
b. Intramolecular, covalent, strengthening
c. Intermolecular, LDF’s, strengthening
4. As the molecules gain energy, they are able to overcome the Coulombic
attractions holding the molecules together.
5. Propane only has weak LDF’s being non-polar while propanol gas both
LDF’s and H-bonds resulting in much stronger coulombic attractions thereby
requiring significantly more energy to break.
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6. Examine the phase diagram below and answer the following questions:
a.
b.
c.
d.
e.
7.
Sublimation and deposition
liquid
373 K
340 K
Condensation and freezing
a. 12,000 Joules
b. 5.71 C
8.
a. Br2 is a covalent molecular solid held by intermolecular forces
which are weak compared to KBr’s strong ionic intramolecular
forces and K’s intramolecular covalent metallic bonds.
b.
i. KBr
ii. K
9.
a. C(diamond) due to it being covalent network and possessing
strong intramolecular covalent bonds between atoms relative to
methane’s weaker intermolecular forces.
b. Copper is a metallic solid with delocalized electrons due to the low
effective nuclear charge of metals compared to the high effective
nuclear charge and subsequent ionization energies of both
covalent molecular methane and covalent network carbon.
10.
a. Density increases, viscosity increases
b. Density decreases, viscosity decreases
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11.
a. Disagree, ionic solids do not conduct
b. Disagree, I2 does have a higher MP but it is due to stronger LDF’s
(an intermolecular force)
c. Agree, wax is a covalent molecular solid
d. Disagree, it is ionic intramolecular forces that are weakening
e. Agree, both metallic but sodium’s larger size gives it weaker
Coulomobic attractions between metal ions.
f. Disagree, liquids densities approximate those of the solid.
g. True, the Coulomobic attractions between liquids and gases permit
the flow of molecules unlike in solids.
h. Disagree, in most covalent molecular solids (excluding noble gas
atoms), there are covalent intramolecular forces within each
molecule.
12.
a.
b.
c.
d.
e.
PH3
SiO2
Cu(OH)2
W
PH3
Teacher Key
13.
a. 2KClO3  2KCl + 3O2
b.
i. 600.8 torr
ii. 23.0 L
iii. 0.0178 moles
iv. 1.33 x slower
14.
a) Oxygen gas is denser due to higher mass, same volumes
b) Same, same temperature
c) Same, same number of moles, volume and temperature = same
pressure
d) F2 would be 1.08 x slower on average due to higher molecular weight
e) F2 gas due to smaller size of molecule. Tough call though really.
15.
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a) 130.3 g/mol
b) C2Cl3H
c) 44.9 g/L
16. 10.3 grams
17.
a) Disagree, the Boltzmann distribution shows a range of speeds at a
given temperature.
b) Disagree, the speeds are inversely proportional to the square root of
the masses
c) Disagree, real gases experience coulombic attractions and therefore
have fewer collisions with the container.
d) Disagree, gases behave most real at low temperatures and high
pressures diminishing the overall container volume and maximizing
coulombic attractions.
e) Agree, water has a higher Coulombic attractions being polar and all.
f) Disagree, the higher the temp, the higher the V, the lower the density.
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