Unit Plan 1: Thermodynamics Shannon B. Carpenter

TE 402 02/09/01

This unit plan is intended to cover two weeks and would be appropriate for an introductory and/or advanced placement chemistry high school class. This unit introduces them to thermodynamics, a topic that they have not yet been introduced to. Central Questions: What is heat? How much heat is evolved during a chemical reaction? If you put a flame to a 2:1 mixture of H2 and O2 there is an almighty bang and the reaction proceeds spontaneously to products, i.e. without any further supply of external energy. Why does it not happen that water spontaneously goes to H2 and O2 if we put a lit paper to it under the same conditions? How does a refrigerator or internal combustion engine work? Science Statements: 1. Energy can be neither created nor destroyed. 2. Heat is particles of matter that have kinetic energy and this kinetic energy transfers from a hotter

object to a colder object. 3. The significance of the entropy change of a reaction determines whether or not it will absorb or

release energy because naturally, reactions will go to a lower Energy State and order. 4. Exothermic and Endothermic are two different ways to explain heat transfer in reactions where

exothermic describes a reaction that releases heat into their surroundings and endothermic reactions absorb heat from their surroundings.

5. Thermodynamics explains these two statements: The rate of a reaction depends on the reaction’s

activation energy and whether or not the reaction will proceed to competition or just a state of equilibrium.

6. In any spontaneous process, the overall entropy of the universe always increases. 7. Energy is released during the forming of bonds and is absorbed during the breaking of bonds. 8. The change in the Gibbs free energy is the maximum work that a spontaneous process can perform.

It is also the minimum work required to carry out a non-spontaneous process. Objectives: * All objectives with an asterisk are ones that are either constructing or reflecting. Source for all objectives: Prentice Hall-Chemistry.

1. Distinguish between exothermic and endothermic replacement reactions.

2. Describe how a calorimeter determines heats of a reaction.

3. Be able to give some examples of heat being produced by the conversion of one form to another.

4. Define standard enthalpy change and explain how it is used.

5. Apply Hess’s law to determine, ∆H° for a reaction.

6. Explain why ∆H for a reaction proportional to the quantity of reactants.

7. Explain what is meant by a spontaneous process.

8. Define entropy.

9. State the entropy and free energy (Gibbs free energy) criterion for a spontaneous process.

10. State the criterion for reaction spontaneity in terms of its free energy change.

11. *Explain what the greenhouse effect is and what can be done to slow it down. 12. *Describe how thermal pollution is affecting our environment and argue for or against whether

or not the government should cut back on energy consumption to help solve this issue. Activities:

1. Lectures. These will be scattered throughout the unit plan with a two discussions focusing on environmental issues such as thermal pollution and greenhouse gases. (All objectives) Knowledge, Modeling

2. *Journal-You and your world-Make a list of the chemical and physical changes taking place

around you for one day. Try to identity them as releasing heat or absorbing heat. After this section is completed, have the students go back to their lists and see if they identified the processes correctly. Source: Prentice Hall-Chemistry. (Obj. 1) Knowledge/Application, Coaching.

3. Laboratory Investigation-Measure the maximum temperatures of a hot and cold pack using a

thermometer. Questions: Which pack produced a greater change in the surrounding temperature? What principle is this reaction based on? What are the advantages of these hot and cold packs over ice packs and hot water bottles? Source: Prentice Hall-Chemistry. (Obj. 1) Knowledge, Modeling

4. *Journal-Connection-Earth Science-Is cloud formation an exothermic or endothermic process?

Explain your reasoning. What happens when raindrops form from clouds? Source: Prentice Hall-Chemistry. (Obj. 1) Application, Coaching

5. *Laboratory Investigation-Heat Effects and Calorimetry-students will be given the specific heat of water in order to find the specific heat of a metal to understand better heat flow. Students will also find the atomic mass of the metal by using the Law of Dulong and Petit. Source: Tom Dubyne, Haslett High School Retired Teacher. (Obj. 2, 4, 5, 11) Knowledge, Coaching

6. *Hess’s Law Handout- This will be for homework. See attached sheet for actual questions.

7. *Laboratory Investigation-Heat of Reaction-Students will experimentally determine the amount

of heat involved when dilute sodium hydroxide reacts with dilute hydrochloric acid. (Students will calculate the total heat gained by the solution and the heat involved per mole of NaOH reacted.) Source: Tom Dubyne, Haslett High School Retired Teacher. (Obj. 1, 5, 11) Knowledge, Modeling/ Coaching

8. Laboratory Investigation-Observing Entropy I-Students will place food coloring in three

different beakers containing water of various temperatures. Questions: Observe what happens. How is entropy influenced by temperature? Source: Prentice Hall-Chemistry. (Obj. 7,8,9) Knowledge, Modeling

9. *Observing Entropy II-Students will use rubber bands and stretch and contract them on their

foreheads in order to determine when heat is being released and absorbed. Students will then be asked to draw diagrams on the molecular level as to what is going on in the rubber band when you do this. (They will be required to use specific concepts in their explanation such as entropy, order, spontaneity, and heat flow.) This will be a homework assignment. Source: http://www.iit.edu/~smile/ph9615.html (Obj. 1, 5, 7, 8, 9,) Application, Fade

10. *Laboratory Investigation-The Heats of Combustion and Solidification-students will discover

that the energy required for a candle to undergo a phase change (change to solid to liquid and vice versa). Students in this lab will calculate the heat of combustion per gram of candle, the heat of solidification per gram of candle and then compare the two to determine what one is larger and by how much. Source: Tammy Voss, East Lansing High School. (Obj. 2, 4, 5, 11) Application, Coaching

11. *Laboratory Investigation- Evaluating Enthalpy and Entropy in Spontaneous Reactions-

Students will observe, based on an increase or decrease in entropy, whether the ∆S and ∆G will be negative or positive for each reaction. Questions: What is the relationship among the three variables (∆H, ∆S and ∆G)? Based on your observations, predict the temperature conditions at which each would be non-spontaneous. Source: Prentice Hall-Chemistry. (Obj. 1, 2, 5, 7, 8, 9, 10, 11) Understanding, Coaching

12. *Chapter 23 Homework Set- See attached sheet for sample problems. (Obj. 9, 10, 11)

Knowledge, Fading

13. Journal-You and Your World-You have learned that in all spontaneous processes, the entropy of the universe always increases. What do you think this means for the future of Earth as well as the future of the universe? Describe your predictions and predict what you think happens to the total energy of the universe over time. Source: Prentice Hall-Chemistry. (Obj. 7,8,9) Application, Coaching

14. *Students will be given a comprehensive exam at the end of the unit covering both Chapters (12 and 23). It will consist of all short answer questions. (All objectives) Knowledge, Application, Understanding

Assessment: Some of my assessment will come from the activities that are asterisked in the above activity list. My formal assessment will be based on about 3 reading pop-quizzes covering main concepts and terminology (multiple choice) and 1 exam covering the two chapters which will be all short answer with some extra credit possibilities.

Sample Test Questions: 1. Juan performed a calorimetry experiment to determine ∆H for the following reaction:

KOH (s) K+ (aq) + OH – (aq)

His calorimeter contained 64.0 g of water at an initial temperature of 20.7°C. When he added 1.65 g of KOH (s) to the calorimeter, the temperature rose to 26.9°C. What value of ∆H can Juan obtain from his data? 2. Carbon dioxide dissolves in water to produce a weak acid, carbonic acid, according to:

CO2(g) + H2O(l) ---> H2CO3(aq)

For this process, ∆Ho = -19.2 kJ and ∆So = -92.0 J/K when 1 mole of CO2 reacts. If CO2(g) is in contact with H2O(l) should a low temperature or a high temperature be used to obtain the largest possible concentration of H2CO3(aq)? Explain.

Hess’s Law Worksheet (Be sure to show all your work!)

1. Calculate ∆H for the following reaction: NiO (s) + 2HCl (g) NiCl2 (s) + H2O (g)

Using the following enthalpy changes:

Reaction ∆H (kJ)

SOCl2 (g) + NiO (s) SO2 (g) +NiCl2 (s) -150

SOCl2 (g) + H2O (g) SO2 (g) +2HCl (g) −27

2. Calculate ∆H for the hydrogenation of ethene to ethane: C2H4(g) + H2(g) → C2H6(g) Using the following enthalpy changes:

Reaction ∆H (kJ)

2H2(g) + O2(g) → 2H2O(l) -571.6

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l) -1411

2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) -3120

3. Calculate ∆H for the formation of nitrous acid: HCl(g) + NaNO2(s) → HNO2(l) + NaCl(s)

Using the following enthalpy changes:

Reaction ∆H (kJ)

2NaCl(s) + H2O(l) → 2HCl(g) + Na2O(s) 507

NO(g) + NO2(g) + Na2O(s) → 2NaNO2(s) -427

NO(g) + NO2(g) → N2O(g) + O2(g) -43

2HNO2(l) → N2O(g) + O2(g) + H2O(l) 34

Chapter 23 Homework Set (Be sure to show all of your work!)

1. The Gibbs free energy change is equal to

(a) ∆H - T∆S (c) ∆G - T∆S (b) ∆H - S∆T (d) ∆H + T∆S

2. In all spontaneous processes

(a) Enthalpy decreases (c) Useful work can be performed (b) Free energy increases (d) Suniverse decreases

True and False: If it is false, change the underlined word(s) to make the statement true. 3. Energy and enthalpy are the two driving forces of chemical and physical reactions. 4. The work performed by a spontaneous reaction is always more than the ∆G for the reaction.

Problems:

1. Predict the sign of ∆ S for the following transformations:

(a) CO2 (s) CO2 (g) (b) NaCl (l) NaCl (s) (c) Hg (l) Hg (g)

2. For the following reactions, predict the sign of ∆S from the nature of the reaction. Then predict if the reaction is spontaneous, non-spontaneous, or dependent on the values of ∆S, ∆H, and temperature.

(a) CaCo3 (s) CaO (s) + CO2 (g) (endothermic) (b) 2NF3 (l) N2 (g) + 3F2 (g) (exothermic) (c) 2XeO3 (s) 2Xe (g) + 3O2 (g) (exothermic)

3. What is the sign of ∆S for each of the following processes? (a) A football stadium empties after a game. (b) A baby develops into an adult. (c) Paper, plastics, and aluminum are separated and recycled.