Unit 4 for the Teacher
Student Prior Understanding
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Historical timeline of the science called chemistry
Atomic structure
Periodicity
Molar mass
Naming ionic and molecular compounds
Molecular Geometry
Stoichiometry
Students will be given a project to focus on at the beginning of this unit so that, as they progress
through the unit, they can put their understanding into practice as they develop their project.
This is a 15 day unit.
The Teacher's Goal: Thermo chemistry
These topics are addressed in this unit
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Specific heat
Q=mcΔT
Calorimetry
Heating curves with phase changes
Enthalpies of reactions
Hess's Law
Entropy
Free energy
Quality Core standards
V.
INTEGRATING THE MACROSCOPIC, MICROSCOPIC, AND SYMBOLIC WORLDS
B.
3.
Kinetics, Equilibrium, and Thermodynamics
Chemical Processes and Heat; Calorimetry
a)
Explain the law of conservation of energy in chemical reactions
b)
Describe the concept of heat, and explain the difference between heat energy and
temperature
c)
d)
e)
4.
f)
g)
h)
i)
Explain physical and chemical changes as endothermic or exothermic energy
changes
Solve heat capacity and heat transfer problems involving specific heat, heat of
fusion, and heat of vaporization
Calculate the heat of reaction for a given chemical reaction when given calorimetric
data
Enthalpy and Entropy
Define enthalpy and explain how changes in enthalpy determine whether a reaction
is endothermic or exothermic
Compute ΔHrxn from ΔHfº values and explain why the ΔHfº values for elements are
zero
Explain and apply, mathematically, the relationship between ΔHrxnº (forward) and
ΔHrxnº (reverse)
Define entropy and explain the role of entropy in chemical and physical changes,
and explain the changes that favor increases in entropy
Unit 4 Learning Targets
1. I can determine the amount of heat gained or lost for a specific substance
2. I can use the heat relationship between two objects to determine missing information in a given
situation where there is heat transfer occurring.
3. I can interpret an enthalpy diagram and decide if a reaction is endothermic or exothermic.
4. I can apply stoichiometric calculations (mass-mole-molar ratio-heat) to equations involving heat.
5. I can apply Hess's Law in order to determine the heat of a reaction
6. I can determine if a reaction is spontaneous using Gibb’s Free Energy
Plan
1. Introduce unit, create rubric for project
2. Discuss 4 Laws of Thermodynamics (1st, 2nd, 3rd, and zeroth) and practice the concept of
specific heat
3. Apply q=mcΔT
4. Perform calorimetry lab 1
5. Perform caliorimetry lab 2
6. Discuss heating curve and relate to phase change diagram
7. Perform stoichiometric calculations including enthalpies with enthalpy diagrams
8. Use stoichimetric calculations, equations, and enthalpy diagrams while applying Hess's Law
9. Hess's Law Lab
10. Introduce entropy
11. Discuss Gibbs Free energy applying calculations and predicting based on signs
Lectures with Assignments
Lectures should last no more than 30 minutes. Lectures are not given every day of the unit. Time each
day should be allowed for students to work on assignments, labs, and research for the project.
Students should be permitted the opportunity to work ahead if so desired, but a schedule should be
provided so that students can stay on track and on pace with the work of the unit. Typically, a good due
date is two days after any given lecture when the assignment has been addressed.
1st lecture
Discuss the laws of thermodynamics. Most students already possess some prior knowledge of these
energy concepts from previous courses. Spend some time focusing on the zeroth law and relate it to the
transitive property in mathematics. The students will need a firm grasp of this concept in order to fully
investigate and understand specific heat problems.
Demonstrate the heating of water. Use a water in a 250ml beaker with a thermometer in it. Heat a
brass ball until near glowing using a propane torch. AS heating is occurring, ask the students to describe
what is happening to the particles in the metal. NOTE: students often confuse energy and temperature.
Temperature is a reflection of average kinetic energy, but it is not energy itself. Ask students to
predict what will happen to the water once the metal is placed in the sample. Drop the hot metal in and
allow the sizzle to occur. Reach in and grab the now cool metal and ask them what the temperature of
the metal is compared to the water. This will set the class up for a good application of the zeroth law
and the 1st law using q=mcΔT.
Explain the heat equation. Perform two calculations using the heat equation.
Assign Specific heat 1 and 2
2nd lecture
Demonstrate the heating of water as it transitions through phases. Prior to class, freeze a sample of
water that has a thermometer in the sample. Heat the sample, tracking the temperature as time
progresses. Point out that the energy is being added in equal units of time, but that the temperature
remains constant at the melting point unit the total sample is melted and the phase change is complete.
Graph the data, noting the phases and phase change. Include the energies and specific heats for heat
phase.
Tech link: http://phet.colorado.edu/en/simulation/states-of-matter
Assign Heating Curve 1 and 2
Lab: Calorimetry 1 and 2
At this point, students should be working on 6 of the 14 required assignments for this unit. It is
necessary that students have an opportunity to work on the assignments and ask questions of the
instructor and other students.
Students should have selected a fuel to investigate for the project. Set a due date for a rough draft of
Report 1 so that they have enough time to get feedback and make changes prior to the end of the unit.
3rd lecture
Review stoichiometry. Include the enthalpy of reaction for an endothermic reaction and an exothermic
reaction. Show the enthalpy diagrams for each and address the key vocabulary of enthalpies.
Rewrite the balanced equations placing the energy into the equation on the appropriate side so that
students can see that it is part of the balanced equation, then explain that writing it off to the side will
make it easier to track and less cumbersome to write. Relate the equation to the graph for every
example given in class. Provide a few opportunities to have the student walk through the process
together as a class
Assign Enthalpies of Reaction 1 and 2
4th lecture
Work with a math teacher in advance. Prepare two examples of solving a system of equations from
math class. Show solving both using graphing, substitution and elimination. Set them up in such a way
to where elimination seems to be the easiest and quickest method.
Explain and model using Hess's law to solve for enthalpies of equations that would otherwise be difficult
to measure. Relate the elimination method to Hess's Law using a simple two equation process.
Prepare 3-4 examples to work through together as a class. Have students write each step down on their
own at their seats and then show the next step on the board. Continue until the problems are complete
and the students a "road map" for solving problems by using Hess's Law.
Tech Link: https://www.dartmouth.edu/~chemlab/info/resources/applets.html
Assign Hess's Law 1 and 2
Lab: Hess's Law
5th lecture
Discuss Entropy. Explain entropy by relating it to the students cleaning their rooms at home and how
they seem to spontaneously become disorderly again. Most can relate to this example and the fact that
it takes energy (work) to get it orderly again.
Check on the progress of the Reports. Set a dues date for Report 2 and ask for a materials list and
procedure for Report 3. Conference and provide feedback for the reports.
6th lecture
Discuss free energy. Prepare several examples in which the free energy equation can be applied. Use
the data from the examples to develop a chart that can used to make predictions based on signs of
enthalpy and entropy.
Tech link: http://chemconnections.org/Java/Gibbs/Gibbs.html
Tech link: http://chemistry.beloit.edu/chip/Gibbs/index.html
Assign Free Energy 1, 2, and 3
Wrapping up
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Plan enough time for the students to make a sample of their fuel.
Plan enough time for the students to receive feedback on their reports so that when the final
draft is submitted, grading will be easy and, essentially, already determined.
Plan for a review session prior giving the unit test.
Sources
Many sources have been around and used by many of us teachers for a long time. As often as possible, I
try to keep the original documents that I have found in their original forms and the authors have stated
their names. Some sources I've had for so long and have long since forgotten from where they came.
Feel free to use anything I have created.