Term 3 – Practice Questions
Grade 09 – Advanced
PHY41
Learning Outcome
Topic 9: Thermal Energy
Subtopic 9.2: Changes of state and Thermodynamics
(KPIs 9.2.1 – 9.2.7)
1. Thermal energy needed to boil a liquid is the heat
of _______.
5. When a gas condenses it _____ heat and its
temperature _____.
A.
condensation
A.
gains heat, temperature decreases
B.
fusion
B.
gains heat, temperature increases
C.
vaporization
C.
loses heat, temperature decreases
D.
specific
D.
loses heat, temperature doesn’t change
6. The heat energy required to change 1 kg of a
substance from a solid to a liquid state at the same
temperature is called ______.
2. The average kinetic energy of ice particles _____ as
ice melts.
A.
decreases
B.
increases
C.
reduces to zero
D.
remains constant
3. When a solid melts it _____.
A.
gains heat and its temperature decreases
B.
gains heat and its temperature increases
C.
loses heat and its temperature decreases
D.
gains heat and its temperature does not
change
An absorption of thermal energy by ice
B.
An increase in temperature
C.
A decrease in temperature
D.
A removal of thermal energy from ice
specific heat capacity
B.
specific latent heat of vaporization
C.
sensible heat
D.
specific latent heat of fusion
7. What is the thermal energy removed to convert
0.5 kg of water at 0°𝐶 to ice at 0°𝐶?
4.. Which of the following always accompanies the
formation of water from ice?
A.
A.
1
A.
0𝐽
B.
1.5 × 10! 𝐽
C.
3.0 × 10! 𝐽
D.
6.0 × 10! 𝐽
8. The table below shows two substances at their
respective melting points. Which of the substances
would melt completely when 300 J of heat is added to
each of them?
Mass
Latent Heat of fusion
Substance A
20 g
1.2 × 10" 𝐽/𝑘𝑔
Substance B
30 g
9.7 × 10# 𝐽/𝑘𝑔
A.
A only
B.
B only
C.
Both A and B
D.
Neither A nor B
12. The figure shows a graph of the temperature of
a pure substance as a function of time as heat is
added to it at a constant rate in a closed container. If
LF is the latent heat of fusion of this substance and
LV is its latent heat of vaporization, what is the
value of the ratio LV/LF?
9. A 50 g of an unknown substance at its melting
point absorbs 8000 J of heat to melt completely.
What is the latent heat of fusion of the substance?
A.
160 J
B.
400 J
C.
40000 J
D.
160000 J
heat is needed to melt it? For water LF = 334,000 J/kg
and LV = 2.256 x106 J/kg.
1.50 ´ 104 kJ
B.
4.10 ´ 106 kJ
C.
0.00 kJ
D.
1.02 ´ 105 kJ
3.5
B.
C.
4.5
5.0
D.
7.2
13. Consider the following temperature-time graph
when a solid is heated. Which part of the graph
involves latent heat of vaporization?
10. A 45.0 kg sample of ice is at 0.00° C. How much
A.
A.
A.
Part I
B.
C.
Part II
Part III
D.
Part IV
14. 1.00 g of ice at –30.0°C is heated and converts to
steam at 120.0°C. The figure below shows how the
temperature changes with the heat added. What is
the energy used to raise the temperature of 1.00 g of
water from 0°C to 100°C?
11. Ice is added to a glass of juice. The temperature of
the juice ______ and the temperature of the ice cubes
__________while they are melting.
A.
decreases
increases
B.
decreases
decreases
C.
decreases
stays constant
D.
stays constant
increases
2
A.
62.7 J
B.
333 J
C.
419 J
D.
2255 J
15. Consider the temperature-heat graph below. If LF
and LV are the latent heat of fusion and vaporization
respectively, what is the ratio 𝐿$ /𝐿% ?
19. In a process, 850 J of heat is added to a system
and 500 J of work is done by the system on its
surroundings. What is the change in internal energy
of the system?
A.
350 J
B.
500 J
C.
850 J
D.
1350 J
20. The internal energy of a system increased by 25 J
while 100 J of heat was added to it. What is work
done by the system?
A.
0.50
B.
0.70
C.
1.0
A.
75 J
D.
1.3
B.
100 J
C.
125 J
D.
2500 J
16. The first law of thermodynamics is a consequence
of ______.
21. The energy input to an engine is 4 times greater
than the work it performs. What is its efficiency?
A.
gravity
B.
conservation of energy
C.
kinetic molecular theory
A.
20%
D.
second law of thermodynamics
B.
25%
C.
75%
D.
80%
17. A system consists of an ice cube floating in water.
The entire system is at 0°𝐶. Thermal energy is then
added to the system, causing half of the ice to melt.
What is the resulting temperature of the system?
22. A heat engine receives 900 J of heat and releases
100 J of heat in each cycle. What is the efficiency of
the engine?
A.
Greater than 0°𝐶
B.
Less than 0°𝐶
A.
11%
C.
Equal to 0°𝐶
B.
25%
D.
Equal to 100°𝐶
C.
75%
D.
89%
18. Which is the example of a heat engine?
A.
solar panels
B.
refrigerator
C.
automobile engine
D.
heat pump
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Questions 23 and 24
An engine has an efficiency of 20% and produces
2000 J of mechanical work during one cycle.
23. How much energy is received by the engine
during one cycle?
25. Which can remove thermal energy from a colder
object and add it to a warmer object?
A.
Microwave
B.
Oven
A.
2000 𝐽
C.
Refrigerator
B.
4000 𝐽
D.
Combustion engine
C.
8000 𝐽
D.
10000 J
26. Which law of thermodynamics states that the
change in thermal energy is equal to the heat added
to the object minus the work done by the object.
24. How much energy is transferred out of the engine
by heating the environment during one cycle?
A.
2000 𝐽
B.
4000 𝐽
C.
8000 𝐽
D.
10000 𝐽
A.
First
B.
Second
C.
Third
D.
Fourth
Answer the following questions
1. A beaker is filled with water and placed on a hot-plate to boil. The hot-plate is on top of a balance, which
measures the mass of water in the beaker. The liquid boils for a long time. There are bubbles within the boiling
water.
a. State what is inside each bubble.
b. The mass of water is measured at two different times, while the water is boiling steadily. Use the below
data to calculate the specific latent heat of vaporization of water, if during this time;
• the mass of water in the beaker decreases by 20 g
• the energy supplied to the hot-plate is 52 000 J
• the energy lost from the hot-plate and beaker to the atmosphere is 6000 J
2. Heat is supplied to convert 1.26 kg of water at 100°𝐶 to steam at 100°𝐶? Latent heat of vaporization of water is
2.26 × 10& 𝐽/𝑘𝑔.
a. What is latent heat, and how does it affect the temperature of a substance?
b. Calculate the heat supplied to convert the water into steam.
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3. How much thermal energy must be removed from 0.96 kg of water at 0°𝐶 to make ice cubes at 0°𝐶? Latent heat
of fusion of ice is 3.35 × 10! 𝐽/𝑘𝑔.
4. How much thermal energy must be added to 0.96 kg of water at 100°𝐶 to make steam at 100°𝐶? Latent heat of
vaporization of water is 2.26 × 10& 𝐽/𝑘𝑔.
5. How much thermal energy must be added to 1.75 kg of copper to change it from a solid at 1358 K to a liquid at
1358 K? Latent heat of fusion of copper is 2.07 × 10! 𝐽/𝑘𝑔.
6. How much energy is required to change a 35.0 g ice cube at -5.00 °C into steam at 115°C?
7. In an isolated container, 250 g of ice at -4.0°C is added to 560 g of water at 45°C.
a. Calculate the energy required to melt the 250 g of ice.
b. Calculate the final temperature of the system at thermal equilibrium.
8. In an isolated container, 320 g of ice at 0.0°C is added to 640 g of water at 22°C.
a. Calculate the energy required to melt the 320 g of ice.
b. Calculate the energy lost by the water to reach its freezing point.
c. How much ice is left when the system reaches equilibrium?
5
9. Liquids A and B are at their freezing temperatures. Thermal energy is then removed until each solidifies. The
amount of heat removed and the mass of each liquid are as follows:
Is the latent heat of fusion of liquid A greater than, less than, or the same as the latent heat of fusion of liquid B?
10. The graph below shows the heating curve for a substance as it changes from solid to gas.
a. Answer the questions in the table below.
What is the melting point of the substance?
What is the boiling point of the substance?
Which segment represents the substance in only solid state?
Which segment represents the substance in only liquid state?
Which segment represents the substance in only gaseous state?
Which segment represents the substance in a combination of both solid and
liquid states?
Which segment represents the substance in a combination of both liquid and
gaseous states?
b. Why does the temperature remain constant during a change of state (phase transition)?
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11. The addition of 9.5 × 10! 𝐽 of thermal energy is required to convert a block of ice at −15°𝐶 to water at 15°𝐶.
What was the mass of the block of ice?
12. Suppose the 1.00 kg of water ice in the figure below begins melting at time zero. Thermal energy is added to
this system at the rate of 12,250 J/s. How much time does it take for the system to reach a temperature of 15°𝐶?
7
13. The graph below shows the heating curve for 1 kg of a material. Use the graph to complete the table below.
Describe what is happening in each of the regions below
Region
Description
A
B
C
D
E
14. A swimmer does 4.3 × 10! 𝐽 of work and gives off 1.7 × 10! 𝐽 of heat during a workout. Determine ∆U, W and Q
for the swimmer.
15. How much heat must be added to a gas that does 10 J of work in an isothermal process?
8
16. During a cycle, an engine draws 3.50 × 10# J of energy from a hot reservoir and releases 2.25 × 10# J of energy
to a cold reservoir.
a. How much work does the engine do in one cycle?
b. Calculate the efficiency of the engine.
17. During a cycle, a 42% efficient engine draws 5.20 × 10# J of energy from a hot reservoir.
a. How much energy is released by the engine in the cold reservoir in one cycle?
b. How much work does the engine do in one cycle?
18. An engine receives 690 J of heat from a hot reservoir and gives off 430 J of heat to a cold reservoir.
a. What is the work done by the engine?
b. What is the efficiency of the engine?
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19. What is the efficiency of an engine that exhausts 870 J of heat in the process of doing 340 J of work?
20. The figures below show two energy diagrams X and Y. Complete the table below to match the diagrams to the
corresponding devices.
Device
Energy Diagrams
Heat engine
Heat pump
Refrigerator
Combustion Engine
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