Alabama Science in Motion
Latent Heat of Fusion Teacher Notes
Latent Heat of Fusion Teacher Notes
Purpose:
The purpose of this experiment is to measure the latent heat of fusion for water using standard calorimeter
techniques. You will be adding ice to room temperature water and measuring the temperature change. Then you
will calculate the latent heat of fusion.
Materials/Equipment:
GLX
Ice in ice bath
Temperature Probe
Room temperature water
Top Loading Balance
Paper Towels
Background:
A physical change of state may be either exothermic or endothermic. An exothermic change releases heat to its
surrounds. An endothermic change absorbs heat from its surroundings.
Vaporization and fusion (melting) are examples of endothermic physical changes. The reverse processes,
condensation and freezing, are exothermic. When steam condenses to water, heat is released to the
surroundings.
Heat is the transfer of energy due to a difference in temperature. Thermal energy is a form of internal energy.
The amount of heat, Q, needed to increase (or decrease) the temperature of a sample of a substance is
proportion to both the temperature change and the mass of the sample: Q = mc(Tf – Ti). The amount of heat
transferred also depends on the substance, and is called the specific heat capacity, c. It is defined as the amount
of heat needed to increase the temperature of one gram of substance by one Celsius degree. The specific heat
(capacity) for water is 4186 J/kg°C.
When heat is absorbed by ice at 0°C, the temperature of the ice does not change. Instead, the ice melts. This
melting is an example of a phase change or change in state. The molecules in a solid are close together and exert
attractive forces on each other. When energy is added these attractive forces are overcome and the molecules
are free to moves. The amount of energy transferred during a phase change depends on the amount of substance
and the thermal properties of the substance. This quantity, latent heat (meaning hidden heat) depends on the
nature of the phase change as well as on the properties of the substance. Latent heat of fusion, Lf, is the term
used when the phase change is from solid to liquids. We can calculate the amount of heat required to melt ice:
Q = mLf, where Lf for water is 3.34 x 105 J/kg. It takes much more energy to melt ice than it does to increase the
temperature, as evident by the values of specific heat and latent heat of fusion.
This experiment uses a technique called calorimetry. This technique uses the conservation of energy. If the
system is thermally isolated from its surroundings (by insulating the container) then the heat released by one
substance will equal the heat absorbed by another and the container. The container is called a calorimeter. In
this experiment, we will use Styrofoam cups and assume it does not absorb any heat. We will also be using
room temperature water to minimize heat lost to the ambient air. For conservation of thermal energy, 0 = Qlost +
Qgained. For this experiment, ice will be added to room temperature water. The ice will melt and increase in
temperature. The room temperature water will lose thermal energy and cool down. The water and ice will then
come to an equilibrium temperature. From conservation of energy; 0 = Qwater + Qmelt ice + Qice. The water will
lose energy and experience a decrease in temperature (-Q) and the ice will melt (+Q) and then increase in
temperature (+Q).
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Alabama Science in Motion
Latent Heat of Fusion Teacher Notes
Considerations:
 Teacher must create an ice bath. In a cooler, place plenty of small ice cubes in a small amount of water and
allow this to sit until the ice bath reaches 0.00°C. This insures the ice is not colder than freezing.
 Teacher should supply enough room temperature water in a large picture or coffee pot so that the water is
room temperature. Most tap water is cooler than room temperature. Water that is cooler than room
temperature will absorb heat from the air introducing experimental error.
 Teacher should supply paper towels for students to dry ice.
 Students should use a spoon to transfer “dried” ice from the paper towel to the Styrofoam cup to avoid
melting the ice with their fingertips.
Preparation:
 Students should be familiar with the heating curve of water and calorimetry.
 Review that when adding the ice to the water the ice first melts at a constant temperature and then the
melted ice will increase in temperature to the equilibrium temperature. Demo this concept by placing a
thermometer in an ice bath and a thermometer in boiling water. Have students read the temperature every
couple of minutes and make observations.
Course of Study (2005)
Physics Core:
Standard 5: Explain the concept of entropy as it relates to heating and cooling, using the laws of
thermodynamics.
 Using qualitative and quantitative methods to show the relationship between changes in heat energy
and changes in temperature.
Extension:
Students could monitor the temperature of the ice bath as it is heated to boiling. They could put their ice bath
into a beaker, place on a hot plate, and monitor the temperature using the GLX. They could generate their own
graph indicated melting and boiling. From this they can verify that during a phase change (melting and
vaporization) the temperature does not change.
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Alabama Science in Motion
Latent Heat of Fusion Teacher Notes
Student Data Sheet
Name _____________________________ Partner’s Name(s) _____________________________________
Period/Block _______________________ Date ___________________
Pre Lab Questions:
1. What should be the temperature of the ice in the ice water bath? Explain your reasoning.
The ice should be at 0.00°C because the ice has had time to warm and is in equilibrium with the water.
The ice is melting and it melts at 0.00°C.
2. Will the temperature of the ice change as it is melting? Explain your reasoning.
The temperature of the ice will remain at 0.00°C as it melts. All the energy is used to break the attractive
forces holding the ice molecules together.
3. Is the melting of ice an endothermic or exothermic process? Is the value of heat (Q) for this process positive
or negative? Explain your answer.
Melting of ice is an endothermic process. The ice is absorbing energy so the value of Q will be positive.
4. Is the cooling of water an endothermic or exothermic process? Is the value of heat (Q) for this process
positive or negative? Explain your answer.
Cooling of water is an exothermic process. The water is losing energy so the value of Q will be negative.
Data:
Ice Initial Temperature, Tice
0.30 °C
Mass Empty Cup, mcup
2.23 g
Mass Cup and Water, mcup+water
107.25 g
Water Initial Temperature, Ti
22.40 °C
Water/Melted Ice Final Temperature, Tf
14.10 °C
Mass Cup + Water + Ice, mcup+water+ice
116.95 g
Calculations:
Mass of Water, mwater
Heat released from Water, Qwater
Mass of Ice, mice
0.10502 kg
-3649 J
0.00970 kg
Heat absorbed by melted Ice, Qice
560 J
Heat absorbed to melt Ice, Qmelt ice
3088 J
Latent Heat of Fusion, Hf
318,000 J/kg
Standard Latent Heat of Fusion, Hf
334,000 J/kg
% Error
May, 2013
4.79 %
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Alabama Science in Motion
Latent Heat of Fusion Teacher Notes
Calculations: Show all your work including formulas and units for numbers.
5. Calculate the mass of the room temperature water as mwater in units of kg.
mwater = mcup+water – mcup
mwater = 107.25 g – 2.23 g = 105.02 g
mwater = 0.10502 kg
6. Calculate the amount of heat removed from the room temperature water as Qwater.
Qwater = mwatercwater(Tf – Ti)
Qwater = 0.10502 kg * 4186 J/kg * (14.10°C – 22.40°C)
Qwater = -3649 J
7. Calculate the mass of the ice added as mice in units of kg.
mice = mcup+water+ice – mcup+water
mice = 116.95 g – 107.25 g = 9.70 g
mice = 0.00970 kg
8. Calculate the amount of heat gained by the ice (after it melted) as it increased in temperature to the final
equilibrium temperature as Qice.
Qice = micecwater(Tf – Tice)
Qice = 0.00970 kg * 4186 J/kg * (14.1°C – 0.30°C)
Qice = 560 J
9. Using the Law of Conservation of Energy, calculate the amount of heat required to melt the ice as Q ice melt.
0 = Qwater + Qice + Qmelt ice
Qmelt ice = -(Qwater + Qice)
Qmelt ice = -(-3644 J + 560 J)
Qmelt ice = 3088 J
10. Calculate the latent heat of fusion (Hf) in units of J/kg.
Qice = miceLf
Lf = Qice/mice
Lf = 3088 J/0.00970 kg
Lf = 3.18 x 105 J/kg
11. Calculate the percent error using the 3.34 x 105 J/kg as the standard heat of fusion for water.
|𝑺𝒕𝒂𝒏𝒅𝒂𝒓𝒅−𝑬𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍|
% Error =
𝒙𝟏𝟎𝟎
𝑺𝒕𝒂𝒏𝒅𝒂𝒓𝒅
% Error =
|𝟑.𝟑𝟒𝒙𝟏𝟎𝟓 𝑱/𝒌𝒈−𝟑.𝟏𝟖𝒙𝟏𝟎𝟓 𝑱/𝒌𝒈|
𝟑.𝟑𝟒𝒙𝟏𝟎𝟓 𝑱/𝒌𝒈
𝒙𝟏𝟎𝟎
% Error = 4.79 %
Questions: Answer the questions in complete sentences. Show all your work for any calculations.
12. Which would more effective in cooling a canned soda; 50 g of ice or 50 g of 0°C water? Explain your
answer in terms of heat.
The ice would absorb more heat cooling the canned soda to a lower temperature. The heat of fusion is
much greater than the specific heat of water.
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Alabama Science in Motion
Latent Heat of Fusion Teacher Notes
13. After a long winter, the top layer of a lake may be frozen. As the warm weather arrives, it may take several
weeks for the air temperature by the lake to reach the temperature farther inland. Explain the reason for this.
The ice will be melting absorbing heat from the air. This will keep the air temperature lower than on
land.
14. As a 24.0 ton piece of glacier melts, how much heat does it absorb from the environment? Assume the
glacier is composed of pure water. 1 ton has a mass of 907.2 kg.
Qice = miceHf
mice =
𝟐𝟒.𝟎 𝒕𝒐𝒏
𝟏
𝒙
𝟗𝟎𝟕.𝟐 𝒌𝒈
𝟏 𝒕𝒐𝒏
= 21,800 kg
Qice = 21,888 kg * 3.34 x 105 J/kg
Qice = 7.28 x 109 J
15. A student fails to dry the ice cubes before placing them into the cup of water. How will the student’s
calculate value for heat of fusion compare to the standard value?
The student’s heat of fusion will be lower than the standard because some of the heat from the room
temperature water will be absorbed by the cold water, reducing the amount of heat absorbed by the ice.
May, 2013
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