Download An Investigation Into Heat Transfer, Cooling Capacities, and Dilution

An Investigation Into Heat Transfer,
Cooling Capacities, and Dilution
BY RENEE CLARY
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H
eat energy experiments are fun
for students, relatively easy to
conduct, use minimal equipment, and can effectively integrate
mathematics. Heat transfer can be
documented through temperature
changes that track energy flow. This
article describes inquiry investigations that verify—or contradict—
claims that rocks can successfully chill
a beverage without diluting it.
The science of heat
Thermal energy results from the kinetic motion of atoms and molecules:
When the particles within an object
move faster, the thermal energy of the
object increases. Heat is the thermal
energy that is transferred between
systems of different temperatures.
The heat of a system is mass dependent, but temperature can be used to
compare how hot or cold an object is,
because it is a measure of the average
energy of the object. When objects of
different temperatures are placed together, heat flows from the warmer
object to the cooler one until thermal
equilibrium is achieved.
The specific heat of a substance is
the amount of heat needed for a unit
mass of the substance (e.g., 1 g) to increase or decrease in temperature by
one degree (e.g., 1°C). Heat is not only
required to raise the temperature of an
object, but it is also involved in phase
changes: A substance requires heat to
move from its solid to its liquid phase.
Different objects and different phases
of the same substance have varying heat capacities. The specific heat
capacity of H2O, for example, is
1 cal/g°C in its liquid phase (water)
and 0.5 cal/gºC in its solid phase (ice).
Because rocks do not undergo phase
changes within the normal temperatures and pressures of our daily lives,
the phase change of ice cubes into water is critical in this experiment: The
energy necessary for the phase change
transfers more of the drink’s heat into
the ice, which makes the drink much
cooler.
The law of conservation of energy
states that the total amount of energy
in isolated systems remains the same.
Therefore, we know that when two
substances of different temperatures
are placed in contact, heat will flow
from the warmer substance to the
cooler one. When they have reached
equilibrium, heat lost is equal to heat
gained.
Cooling a drink: “On the
rocks” versus ice
Can rocks be more efficient at cooling
a beverage than ice? Advertisements
CONTENT AREA
Heat transfer,
conservation of energy
GRADE LEVEL
6–8
BIG IDEA/UNIT
Ice is more effective at
cooling beverages than
rocks (“whiskey stones”)
ESSENTIAL PRE-EXISTING
KNOWLEDGE
Heat flows from warmer
to cooler substances,
and these changes
are documented with
temperature changes
(heat lost = heat gained)
TIME REQUIRED
45 min.
COST
< $30 (three sets of
whiskey stones range
from $20 to $30 )
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state that “whiskey stones” are the perfect way to
cool a drink without diluting it. Like ice, the stones
are cooled in a freezer and put into a beverage. Unlike ice, they do not melt at room temperatures, so no
phase change is involved.
Whiskey stones are made of soapstone, which is
primarily talc that has been metamorphosed through
pressure and heat. Talc is the softest mineral on the
original Mohs hardness scale (Mohs 1, out of 10),
but commercial soapstone is typically Mohs 2.5 or
harder (Figure 1). These rock cubes are inexpensive,
reusable, and nonporous, which decreases the risk of
bacterial growth. A set of nine whiskey stones can be
purchased for under $10, and only two or three sets
will be needed for six to eight lab groups in a classroom of 30 students.
on heat transfer, convection, or conduction, simple
demonstrations and activities that use the PredictShare-Observe-Explain framework are available.
These can help teachers identify students’ alternative conceptions about heat (Brown 2011). A typical
Predict-Share-Observe-Explain sequence involves
•
using students’ prior experiences or knowledge
to introduce a challenging question,
•
introducing the investigation,
•
recording students’ predictions of what will
happen,
•
discussing students’ predictions,
•
conducting the investigation and observing the
results,
Classroom investigation: Ice versus rocks
•
explaining results,
Can soapstone actually cool your drink? In this investigation, students explore whether rocks can chill
a liquid as efficiently as ice cubes, with the added
benefit of not diluting the drink. Students can design
and conduct this experiment as an inquiry activity or
follow a general procedural outline for a fun, guided investigation. If your students need a refresher
•
providing scientific explanations, and
•
following up if needed (Haysom and Bowen
2010).
Give each group of two to four students:
•
2 thermometers,
PELEX; RA’IKE, VIA WIKIMEDIA COMMONS
|FIGURE 1: Talc and soapstone
Talc (left) is a soft mineral easily scratched with your fingernail (Mohs hardness = 1) and has multiple commercial
uses. Soapstone (right) is primarily metamorphosed talc and can have a hardness greater than 1. Commercial
soapstone is typically 2.5 Mohs or more but is always less than 5.5; it can be scratched with a knife.
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BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION
•
2 identical containers
(beaker, large foam cup,
or small foam cup with
aluminum foil on top to
hold the thermometer),
•
a graduated cylinder,
•
2–4 soapstone cubes (placed
in a freezer overnight;
the number of soapstones
should approximate the
volume of a single ice cube
for easy visual comparison;
typically, three stones = one
ice cube),
•
water, and
•
ice (typically one or two ice
cubes per group).
|FIGURE 2: Recording temperature for ice versus rocks
By providing different groups Initial water temperature readings are recorded, then rocks are added to one
with different containers—such container, and an ice cube is added to the other. Temperature readings are
as glass and foam—the groups’ recorded for each container in two-minute intervals for 30 minutes.
results can be compared and
used to facilitate discussions
termine the mass of the ice cube beabout insulating materials.
fore water is added. Alternatively,
(Safety note: Students should
By providing different
they can measure the final volume
wear chemical splash goggles
groups
with
different
of the water in the container after
when conducting the experiment. They should also wear containers—such as glass the ice has completely melted. They
and foam—the groups’
should remember that 1 mL of wainsulated gloves when handling
results can be compared ter has 1 g of mass.)
cold materials.)
After noting the initial temperaFor students who may need
and used to facilitate
ture
of the 50 mL of water (room
additional scaffolding to dediscussions about
temperature at time 0), students then
sign and carry out an investiinsulating materials.
record the temperature within each
gation, you can provide a data
container every two minutes, for 30
collection sheet (see Online
minutes total. One student in each
Supplemental Materials) and
group can be the time keeper, one student can be
simple instructions. We direct students to meathe data collector for the rock-and-water mixture,
sure 50 mL of room temperature water for each
and one student can be the data collector for the icecontainer and place a thermometer in each. Next,
and-water mixture. (Each data collector can write
students record the masses for the soapstones and
down the temperature observed in the assigned
ice cubes used in the experiment. Soapstone cubes
container, or a fourth student in the group can serve
are added to one container, and an ice cube is addas the scribe.)
ed to the other (Figure 2). (Note: Students can de-
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|
At the conclusion of the exFIGURE 3: Sample graph
periment, students graph their
data and interpret the graphs.
An example of collected data
and the resulting graph are
shown in Figure 3. Student
groups then should evaluate the
effectiveness of rock cubes for
cooling liquids. Although students typically learn that ice is
more effective at cooling a liquid,
the melting of ice also results in
a diluted liquid when it is used to
cool any liquid other than water. In Figure 4, for example, the
melting of the ice cube would
add enough water to the liquid
to increase its volume by 62%
(dilution = [original liquid volume] / [final liquid volume]).
Students can evaluate whether This graph was produced during an experiment using ~50 ml water, a 30 g ice
the cooling capacity of ice offsets cube, and three soapstone cubes within glass beakers.
the dilution factor of the original
liquid. This can be accomplished
age containers of similar compositions (e.g., foam,
by asking students to investigate at home whether
glass, waxed paper).
diluting 50 mL of their favorite beverage with water (using the dilution percentage they calculated in
their experiment) will result in a beverage that is still
Classroom extensions: Beat the heat
appetizing.
Students assemble a lab report of their experiIn addition to recording data, determining how
ment and results, which teachers can score usdata should be used for analysis, and constructing
ing Thomas’s (2010) modified rubric (see Online
a graph, students can compare container results,
Supplemental Materials). Teachers should provide
graph class averages, or for differentiated instruction
students with the rubric at the beginning of the
with advanced classes, calculate the amount of heat
experiment so that they are aware of the required
involved in their experiments.
report components of the report. In addition to
submitting lab reports with the data and analyses,
Calculating the heat
groups should also present their results and recomUsing the equations below, students can calculate how
mendations to the class. If groups used different
much heat was removed from the water when it was
types of containers (Figure 4), ask students to comcooled with the rock cubes or the ice cube, at the lowpare group results and determine why differences
est temperature of the water mixture. For example,
exist (Figure 5). Teachers should ask students which
students can answer, “What was the total amount of
variables changed in this experiment (i.e., containheat dissipated when 50 mL of water was cooled from
ers’ composition) and whether they personally
25°C to 22°C using the soapstone rocks?” The amount
experienced different chilling effects with beverof heat removed from the system is calculated using
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BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION
heat lost = mcΔT
where m is the mass of the water, c is the specific heat
capacity, and ΔT is the change in temperature. Therefore, because 50 mL of water has a mass of 50 g, and
water has a specific heat capacity of 1 cal/g-°C,
|FIGURE 4: Ice versus rocks sample data
Different groups can test large foam cups or smaller,
coffee-sized cups with aluminum foil over the top to
hold the thermometer in place.
heat lost, water + rocks = (50 g) × (1 cal/g-°C) ×
(25°C − 22°C)
= 150 cal
How does this compare with the heat lost by 50
mL of water in the water-and-ice mixture, to a low
temperature of 9°C? (Note: Although the melting ice
cube adds water to this system, the calculation is beyond the skill level of most middle school students.)
Using the sample data from Figure 4,
heat lost, water + ice mixture = (50 g) × (1 cal/g-°C)
× (25°C − 9°C)
= 816 cal
Students can also compare the heat removed in
investigations using different containers and mathematically relate the insulating capacities of these
containers. Other activities, such as engineering insulated “penguin homes,” can also extend the concept of heat transfer and heat loss to the atmosphere
(Schnittka, Bell, and Richards 2010).
Additional classroom investigations
Other inquiry investigations can be identified, designed, and conducted with student groups. Some
potential questions that students may answer include:
•
What happens if we change the liquid and
substitute lemonade or milk?
•
Will other solid objects—such as gravel pebbles
or glass marbles—work as well as the soapstone
for cooling a liquid?
Other uses for soapstone cubes
Teachers can also conduct density investigations using cube volumes determined by both direct measurements and displacements. Teachers can also
Water and ice
Volume of water added
50 mL
Mass of beaker
232 g
Mass of beaker and ice
262 g
Mass of ice
30 mL
Freezer temperature
−20°C
Water temperature, initial
25°C
Volume of water, conclusion
80 mL
Water and rocks
Volume of water added
50 mL
Mass of rocks (3)
60 g
Freezer temperature
-20°C
Water temperature
25°C
Volume of water, conclusion
50 mL
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use the soapstone cubes for
mineral investigations (including hardness, or what scratches
soapstone and what soapstone
scratches; and reactivity to vinegar), and students can create
data tables and bar graphs for
the various minerals examined.
|FIGURE 5:
Sample graph using various containers (glass, foam, and foam with foil cover)
with 50 mL water and either an ice cube or three soapstone cubes.
Discussion
In addition to functioning as an
inquiry investigation that requires students to collect, analyze, and graph data, the Beat the
Heat activity also asks them to
evaluate a claim about the effectiveness of rocks in chilling a beverage. Although many students
wrote that having an undiluted
liquid is a positive attribute, most
students still argued against rock
cubes for chilling beverages, primarily because they are less efficient than ice. Therefore, this experiment also conveys
the message that claims should be investigated, and
not taken at face value.
Ice and soapstone investigations can be tailored
for a range of student skills, including student-driven inquiry or guided experimentation, additional differentiation for extended topics, or more advanced
scientific and mathematical concepts. I hope you try
the activities in your own classroom, achieve results
of improved student understanding of heat transfer,
and increase student interest for experimentation.
•
REFERENCES
Brown, P. 2011. Teaching about heat and temperature using
an investigative demonstration. Science Scope 35 (4):
31–35.
Haysom, J., and M. Bowen. 2010. Predict, observe, explain:
Activities enhancing scientific understanding. Arlington,
VA: NSTA Press.
National Governors Association Center for Best Practices and
Council of Chief State School Officers (NGAC and CCSSO).
2010. Common core state standards. Washington, DC:
NGAC and CCSSO.
NGSS Lead States. 2013. Next Generation Science Standards:
For states, by states. Washington, DC: National Academies
Press. www.nextgenscience.org/next-generation-sciencestandards.
Schnittka, C., R. Bell, and L. Richards. 2010. Tried and True:
Save the penguins: Teaching the science of heat transfer
through engineering design. Science Scope 34 (3): 82–91.
Sumrall, W.J., and D. Rock. 2002. The cycles of math and
science. Science Scope 25 (7): 18–22.
Thomas, J.D. 2010. Getting students to be successful,
independent investigators. Science Scope 33 (6): 24–31.
ONLINE SUPPLEMENTAL MATERIALS
Data collection sheet and lab report rubric—www.nsta.org/
scope1704
Renee Clary ([email protected]) is associate professor, graduate coordinator, and director of the Dunn-Seiler Museum
in the Department of Geosciences at Mississippi State University in Mississippi State, Mississippi. She also serves as director of
the EarthScholars Research Group and the 15 Degree Laboratory.
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BEAT THE HEAT! AN INVESTIGATION INTO HEAT TRANSFER, COOLING CAPACITIES, AND DILUTION
Connecting to the Next Generation Science Standards (NGSS Lead States 2013)
• The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid
connections are likely; however, space restrictions prevent us from listing all possibilities.
• The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations
listed below.
Standard
MS-PS3-4: Energy
www.nextgenscience.org/pe/ms-ps3-4-energy
Performance Expectation
MS-PS3-4. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and
the change in the average kinetic energy of the participles as measured by the temperature of the sample
DIMENSIONS
CLASSROOM CONNECTIONS
Science and Engineering Practice
Using Mathematics and Computational Thinking
Students determine the volume of water that results when
ice and soapstones are used to cool a drink.
Disciplinary Core Ideas
PS3.A: Definitions of Energy
• Temperature is a measure of the average kinetic energy of
particles of matter.
Students compare and contrast ice and soapstone as
effective cooling agents in heat transfer experiments.
PS3.B: Conservation of Energy and Energy Transfer
• The amount of energy transfer needed to change the
temperature of a matter samples by a given amount
depends on the nature of the matter, the size of the
sample, and the environment.
Crosscutting Concept
Cause and Effect
Students compare the results of using different containers
to cool water
Connections to the Common Core State Standards (NGAC and CCSSO 2010)
ELA
RST.6-8.3. Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical
tasks.
Math
MP.2. Reason abstractly and quantitatively.
6.SP.B.5. Summarize numerical data sets in relation to their context.
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