Svetlana
Jeff Goett
Introduction to Thermodynamics
New Jersey Core Curriculum Standards
Standard 5.1:
A.
Habits of Mind
1.
When making decisions, evaluate conclusions, weigh evidence, and recognize that
arguments may not have equal merit.
2.
Assess the risks and benefits associated with alternative solutions.
3.
Engage in collaboration, peer review, and accurate reporting of findings.
4.
Explore cases that demonstrate the interdisciplinary nature of the scientific
enterprise.
B.
Inquiry and Problem Solving
1.
Select and use appropriate instrumentation to design and conduct investigations.
2.
Show that experimental results can lead to new questions and further
investigations.
Standards 5.7 B:
2.
Explain that while energy can be transformed from one form to another, the total
energy of a closed system is constant.
3.
Recognize that whenever mechanical energy is transformed, some heat is
dissipated and is therefore unavailable for use.
Subunits:
Subunit (1 day)
Zeroth Law of Thermodynamics
Prior knowledge: Teacher should review transitive property (If A=B and B=C, then A+C)
Objectives: Students will learn the definition of thermal equilibrium.
Key concepts: If A&B in thermal equilibrium, B&C in thermal equilibrium, then A&C in
thermal equilibrium.
Planned Activities:
-Observe two cups of water, one cold and one hot and measure the temperature of each
over time with a digital probe. Another probe will measure the temperature of the room.
Students will note that the water comes to room temperature. Now, the teacher ask the
student’s whether the water and room are in equilibrium After they have done this, the
two cups will be put into thermal contact, and the students will observe that the
temperatures of the water do not change, and the students will observe that the cups of
water are in thermal equilibrium. The teacher will point out that if objects A&B and
B&C are in thermal equilibrium, then A& C are in equilibrium as well which will be
verified by the probe reading.
Assessment questions:
I am making tea. I am pouring hot water into the cup. After sometime the hot water is in
equilibrium with the cup, After that I put a tea bag inside the hot water. And after some
time the teabag is in equilibrium with the hot water. (The teabag is suspended in the
middle and does not touch the cup) What is the obvious conclusion.
Give an example of the real life events that follows zeroth law
How can this law be useful to the scientists?
First Law of Thermodynamics (2 days)
Prior knowledge & skills:
-Given a process, students should be able to identify a system and its boundaries, identify
types of energy in system, and represent with a work-energy bar chart, making certain
that energies are balanced. Should also be able to represent process mathematically.
-Given a collision, students should be able to devise an appropriate system and forces
from outside the system, represent process with momentum-impulse diagram, and
represent process mathematically.
-Students should be familiar with observing data and looking for a pattern in the data.
-Students should be familiar with using observed patterns to form an explanation/model
of a process.
-Students should be familiar with testing a hypothesis or model by predicting value of an
observable in an independent experiment, running experiment, and evaluating prediction.
Objectives:
- From numerous observations and patterns, students will revise current work-energy
model to include energy added to a system through the process of heating.
-Students will represent various processes with work-energy-heating bar charts.
-Students will model the transfer of energy through work and heating on a microscopic
level.
-Students will use PV=nRT, work-energy-heat, and microscopic models to represent
same process in different ways.
Key concepts:
initial energy + energy added to system through work + energy added through heating =
final energy
Planned Activities:
-Observe cold-hot water thermal equilibrium; explain that process of heating
increases/decreases internal energy of liquid; represent process with bar chart for hot
water and one for cold water.
-Observe cork fly out of test tube, explain that force exerted on cork by air causes
acceleration and pressure increased by flame, explain that internal energy of gas
increased by flame through heating and given off through work to cork and represent
with bar charts for gas and cork
- Explain process of work and heating as ways to change internal energy. Learn to
represent with bar chart.
- Observe glass bottle being heated in water, thermometer increasing, remove from water,
balloon inflate and thermometer drop. Explain using PV=nRT, and using energy.
Represent with two energy bar charts.
- Microscopically model gas, predict energy changes for interaction with piston and
interaction with substance of different temperatures. Watch simulations and compare
with predictions.
- Watch aluminum can implosion, explain that energy lost through heating and energy
gained through work, and represent with work-energy-internal energy bar charts. Also
explain with P,V, T, and also with microscopic model.
Possible Difficulties:
-Students may believe heating involves the transfer of a substance, not the transfer of
energy. Students can do: ALG 12.1.3; Students could realize that sun could not transfer a
substance/fluid, but instead energy through light.
-Difficulty with modeling microscopic transfer of kinetic energy through collisions:
Students can simulate these collisions with marbles, blocks, etc.
-Students have difficulties determining when energy added through work and energy
added through heating should be positive or negative. Have the students show that if the
environment does positive work on the system (displacement and force exerted by the
environment on the system are in the same direction), then the energy added to the
system through work is positive. If the system does work on the surroundings, though, it
must lose energy.
Formative Assessment:
-Your friend walks inside the dorm from a cold winter day and shakes your hand. You
notice that her hand feels very cold. Represent this process using work-energy-heating
bar charts for two systems. The first system contains only your friend’s hand. The
second system contains both your hand and your friend’s hand.
-Jeopardy: Describe a process that could be represented with the following work-energy
bar chart:
W
Eint
Q
Eint
To add air to a bicycle tire, you manually compress it inside of a hand pump. How are
Pressure, Volume, and Temperature affected during this process? Represent the process
using work-energy-heating bar charts. Qualitatively describe the effects of the interaction
between the gas molecules and the piston.
Specific heat (1 day)
Prior knowledge & skills:
-students should be able to recognize linear relationships from graphs, represent linear
relationships mathematically, and compare magnitudes of slopes from graphs.
Objectives:
-Students will observe from data that change in temperature varies linearly with energy
added through heating and inversely proportional to mass of object. Students will devise
mathematical representation, Q=mCdelta(T).
-Students will also represent process differently using work-energy-heating bar charts
-Students will devise a testing experiment.
Key concepts:
Change in temperature is linearly proportional to energy added through heating and
inversely proportional to mass of object.
Planned Activities:
-Students will observe the change in temperature of a liquid as a known amount of energy
is added to it through heating. Students will observe how the amount of liquid and type
of liquid effects the rate of temperature change. From these patterns, they will construct
Q=mC*delta(T).
-Students will design an experiment to test this model using a different liquid with known
specific heat capacity. Students must identify & predict the value of a particular
experimental observable and also identify how assumptions will effect their predictions.
Students will run experiment and compare predictions with outcome.
Possible Difficulties:
-Students have difficulties determining when energy added through work and energy
added through heating should be positive or negative. Have the students show that if the
environment does positive work on the system (displacement and force exerted by the
environment on the system are in the same direction), then the energy added to the
system through work is positive. If the system does work on the surroundings, though, it
must lose energy.
Formative Assesment:
-When making tea, you want to raise the temperature .1 kg of water from 20 C to 90 C.
Represent this process using a work-energy-bar chart. How much energy must be added
to the system through heating to do this?
Latent Heat (1 day)
Objectives:
-Using the mathematical model Q=mCdelta(T), students will predict change in
termperature as energy is added. Students will evaluate predictions from data and explain
that energy is used to change phase of substance, therefore energy added during phase
change but no change in temperature.
-Investigating amount of energy needed to melt mass m, students derive Q=mL.
-Students will use model for melting to make predictions for evaporation.
Key concepts:
-Energy is needed to change phase of substance, so energy is added during phase change
without change in temperature. Q=mLvapor Q=mLfusion.
Planned Activities:
- Using their Q=mC*deltaT model, students will predict that energy added to ice will
cause the temperature of the ice to change in linearly.
Running the experiment, students will note that while ice melts, energy is added to the ice
but the temperature does not change. They will develop their model to explain that
energy is needed to change the phase of ice, but does not change its temperature.
Using this, students will predict that during evaporation, the same pattern should be
observed. They will confirm this prediction in an experiment.
Assessment Question:
Suppose that one solid substance A, has stronger chemical bonds between its molecules
than solid substance B. Draw two change in temperature vs. energy added through heat
charts for the process of melting these substances. How do the Lfusion constants for each
compare? Why do you think so?
Entropy (2 days)
Objectives:
-Students will represent a process using work-energy-heating bar charts and also consider
how the usefulness of the energy changes during each process.
-Students will devise pattern that energy tends to go from useful form to unuseful form in
a process and learn that this usefulness is measured using entropy.
-This tendency of usefulness to decrease explains why some processes are irreversible
Key concepts:
While energy is conserved in a process, usefulness of energy tends to decrease, making
process irreversible.
Planned Activities:
-Students will consider several processes, representing them using work-heating-energy
bar charts, evaluating ability of each type of energy to be transformed into another type of
energy or into work, and finally, determine whether the process is reversible or
irreversible. Students will observe pattern that a process that transforms energy into an
unuseful type is irreversible, whereas a process that transforms energy into a useful type
is reversible. In all cases, students will observe that energy is conserved.
Possible Difficulties:
-Students will have a difficult time identifying useful and unuseful forms of energy.
Using blocks, springs, flame, piston, demonstrate that some energy can be transferred
into other forms of energy with varying degrees of ease. Show that thermal energy in
wood/ room-temperature table is very difficult to transfer to other types of energy.
Assessment Questions:
-Describe an irreversible process not mentioned in these exercises. What are the initial
and final forms of energy? How does the usefulness of the energy to do mechanical work
change from the initial situation to the final situation?
-Consider the process of a car burning gasoline. Represent this process using a workenergy diagram. Does the useful of the energy to do mechanical work change from the
initial to final state?
Unit Exam:
1) Substances A and B are in thermal equilibrium. Substances B and C are in
thermal equilibrium as well. If substances A and C are put in thermal contact, how do
their temperatures change?
Answer: By the zeroth law of thermodynamics, substances A and C are in thermal
equilibrium. Therefore, they are at the same temperature and will not change
temperatures.
2) Consider water being heated by a coffee machine. Take the water as your system.
Represent this process using a work-energy bar chart.
Answer:
Qcoffee-maker ΔEint
Explain on a microscopic scale how the coffee machine changes the internal
energy of the water.
Answer: The heating element causes the molecules of coffee maker on the coffee
maker-water interface to vibrate. Collisions between these vibrating molecules
and the slower moving water molecules speeds up the water molecules, increasing
their kinetic energy and hence the water’s internal energy.
3) .5 kg of ice is added to 1 kg of water at 100 C. Will all the ice melt? Why?
Answer:
Yes, all the ice will melt. .5 kg of ice needs mLfusion = 167 kJ of energy to melt.
If water decreases its temperature to 0 C, though it will release 418 kJ of energy,
more than enough to melt all of the ice. Infact, there is enough left over energy to
raise the temperature of the water created by the melting to a higher temp.
4) Steve drops a rock onto a piston which compresses the gas in a chamber. The
rock, gas, and piston are in your system. Represent this process using a work-
energy-heating bar chart. Does the entropy of the system increase, decrease, or
remain constant? Why?
Answer:
Ug
ΔEint
Gravitational potential energy is more useful for doing work than internal energy, so
the usefulness of the energy has decreased, and as a result, the entropy of the system
has increased.
Laboratory Activity 1
Purpose: To observe a system on which the work is being done and to analyze this
situation on a microscopic and macroscopic scale.
Materials:
Glass Bottle
Balloon
Lighter
Container with Hot Water
Test tube with Cork
Procedure :
Part A
Take a glass bottle and put a balloon on its neck. Put this glass bottle into a container
with hot water. Observe what happens.
Part B
Take a test tube secure a cork onto it, place it next to flame from a lighter and observe
what happens.
Analysis:
Part
1
2
Describe your outcome
Draw work-energy Bar (modify if
necessary)
Part
1
2
Describe what happens to the system
1
Microscopically
Macroscopically
(use Ideal Gas Law)
Conclusion: What have you learn from this experiment?
2
Laboratory Activity 2
Purpose: To observe states of matter conceptually and mathematically.
Materials:
Ice
Glass Pyrex Beaker
Heating Element
Thermometer
Time clock
Procedure:
First of all, obtain the weight of the beaker. Then, place about 200g of ice into the
previously weighed beaker and weigh it again, in order to obtain the weight of the ice.
Measure temperature of the ice at that moment. It is very important that at this stage all
of the ice is in the solid form and no water is present. Place the beaker with ice onto the
heating element and using time clock take temperature readings every 30s.
Time (sec)
30
60
90
120
150
180
210
240
270
300
330
360
390
420
450
480
510
540
570
600
630
660
690
Temperature (C)
720
750
780
810
840
870
900
Analysis:
1. Design a graphical Representation of the Data collected above. Make sure to
remember which variable is independent and which one is dependant.
2. Divide the graph into stages. Identify an average slope with which the state of the
(ice/water/vapor) changed.
3. Why are the slopes different? And what does it mean? (Hint what physical
process is the clock reading is related to?)
4. Using Handbook of Chemistry and Physics available in the classroom. Look up
the value for the Specific Heat of Water.
5. Calculate the energy transferred through heating from the heating element in
order to warm up the ice until the first drop of water appeared.
6. Calculate the energy transferred through heating provided by the heating element
in order to melt the ice.
7. Calculate the energy transferred through heating provided by the heating element
in order to warm up the water until the first vapor could be observed.
8. Calculate the energy transferred through heating provided by the heating element
in order to evaporate all of the water.
9. Calculate the total energy transferred through heating from the heating plate to the
water.
Conclusion: What have you learned from performing this experiment?