States Of Matter
Teacher Answer Key
March 01, 2012
'see explanation below'
1. Base your answer on the information below and the accompanying table.
A substance is a solid at 15°C. A student heated a sample of the solid substance and recorded the
temperature at one-minute intervals in the accompanying data table.
What is the evidence that the average kinetic energy of the particles of this substance is increasing
during the first three minutes?
Temperature is related to the average kinetic energy of the particles. Since the temperature is
increasing during the first three minutes, the average kinetic energy of the particles is also
increasing.
'see explanation below'
2. Base your answer on the information below and the accompanying table.
A substance is a solid at 15°C. A student heated a sample of the solid substance and recorded the
temperature at one-minute intervals in the accompanying data table.
The heat of fusion for this substance is 122 joules per gram. How many joules of heat are needed to
melt 7.50 grams of this substance at its melting point?
The heat of fusion is the amount of heat needed to melt 1 gram of substance at its melting point. The
solution is shown in the accompanying image:
'see explanation below'
3. Base your answer on the information below and accompanying diagrams.
Cylinder A contains 22.0 grams of CO2(g) and cylinder B contains N2(g). The volumes, pressures,
and temperatures of the two gases are indicated under each cylinder.
Explain why the number of molecules of N2(g) in cylinder B is the same as the number of molecules
of CO2(g) in cylinder A.
According to Avogadro's principle, equal volumes of gases at the same pressure and temperature
contain equal numbers of particles. The pressure, volume, and temperature of both containers of
gases are the same.
'see explanation below'
4. Base your answer on the information below and accompanying diagrams.
Cylinder A contains 22.0 grams of CO2(g) and cylinder B contains N2(g). The volumes, pressures,
and temperatures of the two gases are indicated under each cylinder.
The temperature of the CO2(g) is increased to 450. K and the volume of cylinder A remains constant.
On a separate piece of paper, show a correct numerical setup for calculating the new pressure of the
CO2(g) in cylinder A.
Use the combined gas law equation found on Reference Table T:
Note that only the setup is necessary, not the numerical solution.
'see explanation below'
5. Base your answer on the information below.
A piece of magnesium ribbon is reacted with excess hydrochloric acid to produce aqueous
magnesium chloride and hydrogen gas. The volume of the dry hydrogen gas produced is 45.6
milliliters. The temperature of the gas is 293 K, and the pressure is 99.5 kilopascals.
Calculate the volume this dry hydrogen gas would occupy at STP. Your response must include both
a correct numerical setup and the calculated result. [2]
Use the information provided on Reference Table A and the combined gas law formula on Reference
Table T:
One point is awarded for a correct numerical setup, and one point is awarded for a calculation
consistent with the numerical setup. [2 points]
'see explanation below'
6. Base your answer on the information below.
In a laboratory, a glass tube is filled with hydrogen gas at a very low pressure. When a scientist
applies high voltage between metal electrodes in the tube, light is emitted. The scientist analyzes the
light with a spectroscope and observes four distinct spectral lines. The accompanying table gives the
color, frequency, and energy for each of the four spectral lines. The unit for frequency is hertz, Hz.
Identify one condition not mentioned in the passage, under which hydrogen gas behaves most like
an ideal gas. [1]
Hydrogen behaves most like an ideal gas at low-pressures and high temperatures. The low-pressure
condition was mentioned in the first sentence of the passage. Therefore, the condition not mentioned
is high temperature. [1 point]
'see explanation below'
7. Base your answer on the information below.
When a person perspires (sweats), the body loses many sodium ions and potassium ions. The
evaporation of sweat cools the skin.
After a strenuous workout, people often quench their thirst with sports drinks that contain NaCl and
KCl. A single 250.-gram serving of one sports drink contains 0.055 gram of sodium ions.
Describe the transfer of energy between the skin and the surroundings as a person perspires and the
sweat evaporates. [1]
As the perspiration evaporates, heat flows from the skin to the surroundings. [1 point]
'see explanation below'
8. Base your answer on the information below.
Biodiesel is an alternative fuel for vehicles that use petroleum diesel. Biodiesel is produced by
reacting vegetable oil with CH3OH. Methyl palmitate, C15H31COOCH3, a compound found in
biodiesel, is made from soybean oil. One reaction of methyl palmitate with oxygen is represented by
the balanced equation below.
2C15H31COOCH3 + 49O2 → 34CO2 + 34H2O + energy
State evidence from the balanced equation that indicates the reaction is exothermic. [1]
In an exothermic reaction, energy is released. The equation shows that energy is a product of the
reaction, which means the reaction is exothermic. [1 point]
'see explanation below'
9. Base your answer on the information below.
A method used by ancient Egyptians to obtain copper metal from copper(I) sulfide ore was heating
the ore in the presence of air. Later, copper was mixed with tin to produce a useful alloy called
bronze.
Calculate the density of a 129.5-gram sample of bronze that has a volume of 14.8 cubic centimeters.
Your response must include a correct numerical setup and the calculated result. [2]
Use the density formula given on Reference Table T: (see image)
One point is awarded for a correct numerical setup, and one point is awarded for a calculation that is
consistent with the numerical setup. [2 points]
'see explanation below'
10. Base your answer on the information below.
Natural gas is a mixture that includes butane, ethane, methane, and propane. Differences in boiling
points can be used to separate the components of natural gas. The boiling points at standard pressure
for these components are listed in the accompanying table.
Identify a process used to separate the components of natural gas. [1]
The components of natural gas can be separated because of the differences in their boiling points.
The process is known as fractional distillation.
[1 point]
4
11. A thermometer is in a beaker of water. Which statement best explains why the thermometer
reading initially increases when LiBr(s) is dissolved in the water?
1. The entropy of the LiBr(aq) is greater than the 3. The dissolving of the LiBr(s) in water is an
entropy of the water.
endothermic process.
2. The entropy of the LiBr(aq) is less than the
4. The dissolving of the LiBr(s) in water is an
entropy of the water.
exothermic process.
4 The increase in the thermometer reading indicates that heat has been released during the dissolving
process (that is, the process is exothermic). An inspection of Reference Table I confirms this
observation.
Wrong Choices Explained:
(1), (2) Entropy changes are based solely on changes in disorder.
4
12. Which process increases the potential energy of the particles of a sample?
1. condensation
3. solidification
2. deposition
4. vaporization
4 The following phase changes cause the potential energy of a substance to increase: solid to liquid
(melting or fusion), solid to gas (sublimation), and liquid to gas (boiling or vaporization).
2
13. Which sample at STP has the same number of molecules as 5 liters of NO2(g) at STP?
1. 5 grams of H2(g)
3. 5 moles of O2(g)
2. 5 liters of CH4(g)
4. 5 x 1023 molecules of CO2(g)
2 According to Avogadro's hypothesis, equal volumes of gases at the same temperature and pressure
contain equal numbers of molecules. Of the choices given, only choice (2), 5 liters of CH4(g),
fulfills this requirement.
2
14. Under which conditions of temperature and pressure does oxygen gas behave least like an ideal
gas?
1. low temperature and low pressure
3. high temperature and low pressure
2. low temperature and high pressure
4. high temperature and high pressure
2 Real gases deviate most from ideal behavior when intermolecular attractions are present and/or
when the molecular volume is not negligible, that is, when the molecules are close to one another.
These conditions will be most apparent when the temperature is low and the pressure is high.
3
15. An iron bar at 325 K is placed in a sample of water. The iron bar gains energy from the water if
the temperature of the water is
1. 65 K
3. 65oC
2. 45 K
4. 45oC
3 Use the temperature equation on Reference Table T to calculate the Celsius temperature of the iron
bar: The bar will absorb heat only from water that is at a higher temperature than the iron: 65oC.
4
16. A 1.0-gram sample of which element will uniformly fill a closed 2.0-liter container at STP?
1. antimony
3. tellurium
2. sulfur
4. xenon
4 Only gases fill the entire container in which they are enclosed. See the melting and boiling point
columns on Reference Table S. Of the choices given, only choice (4), xenon, is a gas at STP.
Wrong Choices Explained:
(1), (2), (3) Antimony, sulfur, and tellurium are solids.
1
17. A sample of gas occupies a volume of 50.0 milliliters in a cylinder with a movable piston. The
pressure of the sample is 0.90 atmosphere and the temperature is 298 K. What is the volume of the
sample at STP?
1. 41 mL
3. 51 mL
2. 49 mL
4. 55 mL
1 Use Reference Table A and the combined gas law equation on Reference Table T:
3
18. Which term is defined as a measure of the average kinetic energy of the particles in a sample of
matter?
1. activation energy
3. temperature
2. potential energy
4. entropy
3 According to the kinetic-molecular theory (KMT) of matter, the temperature of a sample of matter
is a measure of the average kinetic energy of the particles of the sample.
3
19. Under which conditions of temperature and pressure does a sample of neon behave most like an
ideal gas?
1. 100 K and 0.25 atm
3. 400 K and 0.25 atm
2. 100 K and 25 atm
4. 400 K and 25 atm
3 Real gases behave most ideally when the volume of the gas particles is negligible and the particles
have enough kinetic energy to overcome intermolecular forces. These occur under conditions of
high temperatures and low pressures. Of the choices given, choice (3), 400 K and 0.25 atm, has the
highest temperature and the lowest pressure.
2
20. According to the kinetic molecular theory, which statement describes the particles in a sample of
an ideal gas?
3. The collisions between the gas particles cannot
1. The force of attraction between the gas
result in a transfer of energy between the
particles is strong.
particles.
4. The separation between the gas particles is
2. The motion of the gas particles is random and
smaller than the size of the gas particles
straight-line.
themselves.
2 The following assumptions form the basis of the kinetic-molecular theory:




Intermolecular forces between the gas particles are negligible.
The gas particles move in random, straight-line motion.
All collisions between the gas particles are elastic, that is, energy is conserved.
The separation between the gas particles is much larger than the size of individual particles.
3
21. Which statement describes the transfer of heat energy that occurs when an ice cube is added to
an insulated container with 100 milliliters of water at 25oC?
1. Both the ice cube and the water lose heat
3. The ice cube gains heat energy and the water
energy.
loses heat energy.
2. Both the ice cube and the water gain heat
4. The ice cube loses heat energy and the water
energy.
gains heat energy.
3 Heat represents the transfer of energy from a material at a higher temperature to one at a lower
temperature. Since the temperature of the water is higher than the temperature of the ice cube, heat
energy is lost by the water and gained by the ice cube.
4
22. Which graph represents the relationship between pressure and volume for a sample of an ideal
gas at constant temperature?
4 At constant temperature, the pressure of an ideal gas is inversely proportional to its volume. As the
pressure increases, the volume decreases and vice versa. Of the choices given, only the graph in
choice (4) displays this trend.
2
23. Object A at 40.oC and object B at 80.oC are placed in contact with each other. Which statement
describes the heat flow between the objects?
3. Heat flows in both directions between the
1. Heat flows from object A to object B.
objects.
2. Heat flows from object B to object A.
4. No heat flow occurs between the objects.
2 Heat flow between two objects depends on their temperatures. Heat flows from the object with the
higher temperature to the object with the lower temperature. Since the temperature of object B is
higher than the temperature of object A, heat will flow from B to A.
4
24. Which sample has particles with the lowest average kinetic energy?
1. 1.0 g of I2 at 50.oC
3. 7.0 g of I2 at 40.oC
2. 2.0 g of I2 at 30.oC
4. 9.0 g of I2 at 20.oC
4 The average kinetic energy of the particles of a sample depends solely on the temperature of the
sample. The lower the temperature, the lower the average kinetic energy of the particles. Of the
choices given, choice (4), 9.0 g of I2 at 20oC, has the lowest temperature and, therefore, the lowest
average kinetic energy.
2
25. Which gas sample at STP has the same total number of molecules as 2.0 liters of CO2(g) at STP?
1. 5.0 L of CO2(g)
3. 3.0 L of H2S(g)
2. 2.0 L of Cl2(g)
4. 6.0 L of He(g)
2 Avogadro's hypothesis states that equal volumes of gases at the same temperature and pressure
contain equal numbers of molecules. All of the gases in this question are at STP. In other words,
they are all at the same temperature and pressure. Of the choices given, only choice (2), 2.0 L of
Cl2(g), occupies the same volume as 2.0 L of CO2.
4
26. Petroleum can be separated by distillation because the hydrocarbons in petroleum are
1. elements with identical boiling points
3. compounds with identical boiling points
2. elements with different boiling points
4. compounds with different boiling points
4 Distillation is used to separate mixtures that contain substances with different boiling points.
Hydrocarbons are compounds, not elements.
4
27. A gas sample is at 25oC and 1.0 atmosphere. Which changes in temperature and pressure will
cause this sample to behave more like an ideal gas?
1. decreased temperature and increased pressure 3. increased temperature and increased pressure
2. decreased temperature and decreased pressure 4. increased temperature and decreased pressure
4 Real gases behave most ideally when their molecules are far enough apart to make their molecular
volumes negligible (low pressure) and are moving fast enough to overcome any intermolecular
forces (high temperature).
2
28. A cylinder with a movable piston contains a sample of gas having a volume of 6.0 liters at 293 K
and 1.0 atmosphere. What is the volume of the sample after the gas is heated to 303 K, while the
pressure is held at 1.0 atmosphere?
1. 9.0 L
3. 5.8 L
2. 6.2 L
4. 4.0 L
2 Use the combined gas law equation found on Reference Table T: (see image)
3
29. What is the minimum amount of heat required to completely melt 20.0 grams of ice at its
melting point?
1. 20.0 J
3. 6680 J
2. 83.6 J
4. 45 200 J
3 Use the heat of fusion of ice given on Reference Table B and the heat of fusion equation found on
Reference Table T: (see image)
1
30. Which equation represents sublimation?
1. I2(s) --> I2(g)
3. I2(l) --> I2(g)
2. I2(s) --> I2(l)
4. I2(l) --> I2(s)
1 Sublimation is the phase change from solid to gas, as illustrated in the equation shown in choice
(1).
Wrong Choices Explained:
(2) This equation represents melting or fusion.
(3) This equation represents boiling or vaporization.
(4) This equation represents freezing or solidification.
2
31. Which sample of ethanol has particles with the highest average kinetic energy?
1. 10.0 mL of ethanol at 25oC
3. 100.0 mL of ethanol at 35oC
2. 10.0 mL of ethanol at 55oC
4. 100.0 mL of ethanol at 45oC
2 The average kinetic energy of the particles of a sample of matter is directly related to its
temperature. The volume of the sample is irrelevant. Of the choices given, choice (2), 10.0 mL of
ethanol at 55oC, has the highest temperature. Therefore, the particles in this sample have the highest
average kinetic energy.
2
32. A real gas behaves least like an ideal gas under the conditions of
1. low temperature and low pressure
3. high temperature and low pressure
2. low temperature and high pressure
4. high temperature and high pressure
2 Real gases behave least ideally when they are subject to intermolecular forces and the volume of
the gas particles is no longer negligible. These two conditions occur when the gas particles are made
to move more slowly and are allowed to approach each other more closely, i.e., at low temperature
and high pressure.
1
33. Which sample of matter can be separated into different substances by physical means?
1. LiCl(aq)
3. NH3(g)
2. LiCl(s)
4. NH3(l)
1 Only mixtures can be separated into different substances by physical means. Of the choices given,
only choice (1), LiCl(aq), is a mixture. It is an aqueous solution of LiCl.
4
34. Which statement describes the particles of an ideal gas?
1. The particles move in well-defined, circular
3. There are forces of attraction between the
paths.
particles.
2. When the particles collide, energy is lost.
4. The volume of the particles is negligible.
4 An ideal gas consists of particles that have negligible volumes. These particles also have mass;
move in random, constant, straight-line motion; undergo perfectly elastic collisions; and have no
attraction for each other, except during collisions.
2
35. A sample of gas confined in a cylinder with a movable piston is kept at constant pressure. The
volume of the gas doubles when the temperature of the gas is changed from
1. 400. K to 200. K
3. 400.oC to 200.oC
2. 200. K to 400. K
4. 200.oC to 400.oC
2 Use the combined gas law equation on Reference Table T. At constant pressure, this equation
reduces to: (see image) where the temperature is always measured in kelvins (K). If the Kelvin
temperature doubles, the volume of the gas will double. Choice (2) reflects a doubling of the Kelvin
temperature.
Wrong Choices Explained:
(1) This change will reduce the volume to one-half its original value.
(3), (4) Celsius temperatures are never used in gas law problems.
1
36. The temperature of a sample of matter is a measure of the
1. average kinetic energy of its particles
3. total kinetic energy of its particles
2. average potential energy of its particles
4. total potential energy of its particles
1 According to the kinetic-molecular theory, the temperature of a sample of matter is a measure of
the average kinetic energy of its particles.
4
37. According to the kinetic molecular theory, the particles of an ideal gas
3. are arranged in a regular, repeated geometric
1. have no potential energy
pattern
4. are separated by great distances, compared to
2. have strong intermolecular forces
their size
4 According to the kinetic-molecular theory, an ideal gas consists of particles that:





have mass.
are separated by great distances compared to their size.
move in random, constant, straight-line motion.
undergo perfectly elastic collisions.
have no attraction for each other, except during collisions.
4
38. In a laboratory where the air temperature is 22oC, a steel cylinder at 100.oC is submerged in a
sample of water at 40.oC. In this system, heat flows from
3. the air to the water and from the water to the
1. both the air and the water to the cylinder
cylinder
4. the cylinder to the water and from the water to
2. both the cylinder and the air to the water
the air
4 Heat flows from a body at higher temperature to a body at a lower temperature. Since the cylinder
is at a higher temperature than the water, heat flows from the cylinder to the water. Since the water
is at a higher temperature than the air, heat flows from the water to the air.
2
39. Which temperature change would cause a sample of an ideal gas to double in volume while the
pressure is held constant?
1. from 400. K to 200. K
3. from 400.oC to 200.oC
2. from 200. K to 400. K
4. from 200.oC to 400.oC
2 Use the combined gas law equation on Reference Table T. At constant pressure, this equation
reduces to: (see image)
The temperature is always measured in kelvins (K). If the Kelvin temperature doubles, the volume
of the gas will double. Choice (2) reflects a doubling of the Kelvin temperature.
Wrong Choices Explained:
(1) This change will reduce the volume to one-half its original value.
(3), (4) Celsius temperatures are never used in gas law problems.
3
40. A 36-gram sample of water has an initial temperature of 22oC. After the sample absorbs 1200
joules of heat energy, the final temperature of the sample is
1. 8.0oC
3. 30.oC
2. 14oC
4. 55oC
3 Use Reference Table B and the first heat equation on Reference Table T:
(see image)
2
41. The graph (see image) represents the uniform heating of a substance, starting with the substance
as a solid below its melting point.
Which line segment represents an increase in potential energy and no change in average kinetic
energy?
2 Since heat is continually absorbed by the substance, the potential energy and/or the average kinetic
energy continually increase. When the temperature of the substance remains constant, as during a
phase change, the potential energy increases but the average kinetic energy does not increase. This
occurs over segments BC and DE.
2
42. A real gas differs from an ideal gas because the molecules of real gas have
1. some volume and no attraction for each other 3. no volume and no attraction for each other
2. some volume and some attraction for each
4. no volume and some attraction for each other
other
3
43. Which temperature change would cause the volume of a sample of an ideal gas to double when
the pressure of the sample remains the same?
1. from 200oC to 400oC
3. from 200 K to 400 K
o
o
2. from 400 C to 200 C
4. from 400 K to 200 K
1
44. The temperature at which the solid and liquid phases of matter exist in equilibrium is called its
1. melting point
3. heat of fusion
2. boiling point
4. heat of vaporization
2
45. A 3.00-liter sample of gas is at 288 K and 1.00 atm. If the pressure of the gas is increased to 2.00
atm and its volume is decreased to 1.50 liters, the Kelvin temperature of the sample will be
1. 144 K
3. 432 K
2. 288 K
4. 576 K
4
46. Fractional distillation is a technique used to separate complex mixtures of hydrocarbons based
on differences in their
1. heats of fusion
3. melting points
2. heats of vaporization
4. boiling points
3
47. A student observed that the temperature of water increased when a salt was dissolved in it. The
student should conclude that dissolving the salt caused
1. formation of an acidic solution
3. an exothermic reaction
2. formation of a basic solution
4. an endothermic reaction
1
48. A dry mixture of KNO3 and sand could be separated by
1. adding water to the mixture and filtering
3. heating the mixture to a high temperature
2. adding water to the mixture and evaporating
4. cooling the mixture to a low temperature
3
49. Which 5.0-milliliter sample of NH3 will take the shape of and completely fill a closed 100.0milliliter container?
1. NH3(s)
3. NH3(g)
2. NH3(l)
4. NH3(aq)
1
50. Which graph shows the pressure-temperature relationship expected for an ideal gas?
1
51. At the same temperature and pressure, which sample contains the same number of moles of
particles as 1 liter of O2(g)?
1. 1 L Ne(g)
3. 0.5 L SO2(g)
2. 2 L N2(g)
4. 1 L H2O(l)
3
52. Which change in the temperature of a 1-gram sample of water would cause the greatest increase
in the average kinetic energy of its molecules?
1. 1oC to 10oC
3. 50oC to 60oC
2. 10oC to 1oC
4. 60oC to 50oC
2
53. As ice melts at standard pressure, its temperature remains at 0oC until it has completely melted.
Its potential energy
1. decreases
3. remains the same
2. increases
2
54. Using the given diagram:
Which diagram represents a mixture?
4
55. In which material are the particles arranged in a regular geometric pattern?
1. CO2(g)
3. H2O(l)
2. NaCl(aq)
4. C12H22O11(s)
1
56. Which change is exothermic?
1. freezing of water
2. melting of iron
3. vaporization of ethanol
4. sublimation of iodine
2
57. Which statement correctly describes an endothermic chemical reaction?
1
58. Recovering the salt from a mixture of salt and water could best be accomplished by
1. evaporation
3. paper chromatography
2. filtration
4. density determination
*1 Salt is nonvolatile, and evaporating the water would leave the salt behind.
*Since the question did not make clear whether the salt was completely dissolved in the water, credit
is also allowed for choice (2), filtration.
2
59. The average kinetic energy of water molecules is greatest in which of these samples?
1. 10 g of water at 35°C
3. 100 g of water at 25°C
2. 10 g of water at 55°C
4. 100 g of water at 45°C
2 The average molecular kinetic energy of a collection of molecules depends solely on the
temperature of the substance: the higher the temperature, the greater the average molecular kinetic
energy.
3
60. Helium is most likely to behave as an ideal gas when it is under
1. high pressure and high temperature
3. low pressure and high temperature
2. high pressure and low temperature
4. low pressure and low temperature
3 A gas behaves most ideally when intermolecular attractions are at their lowest. At low pressures,
the molecules are farther apart and are less able to form significant intermolecular attractions. At
high temperatures, the greater average kinetic energy (that is, speed) of the molecules prevents the
molecules from forming significant intermolecular attractions.
4
61. At STP, the element oxygen can exist as either O2 or O3 gas molecules. These two forms of the
element have
3. different chemical properties and the same
1. the same chemical and physical properties
physical properties
2. the same chemical properties and different
4. different chemical and physical properties
physical properties
4 Since the bonding in O2 and O3 are different, these forms of oxygen behave differently, both
physically and chemically.
4
62. Which sample contains particles in a rigid, fixed, geometric pattern?
1. CO2(aq)
3. H2O(l)
2. HCl(g)
4. KCl(s)
4 Particles arranged in a rigid, fixed, geometric pattern are characteristic of the solid phase.
3
63. A sealed flask containing 1.0 mole of H2(g) and a sealed flask containing 2.0 moles of He(g) are
at the same temperature. The two gases must have equal
1. masses
3. average kinetic energies
2. volumes
4. numbers of molecules
4
64. Two basic properties of the gas phase are
1. a definite shape and a definite volume
2. a definite shape but no definite volume
3. no definite shape but a definite volume
4. no definite shape and no definite volume