Title of Lesson: Cold Pack Chemistry

UFTeach Student’s Name: Julie KnoxTeaching Date and Time: March 28-29, 11:05-11:55 amLength of Lesson: 2 days (50 minute class period per day)Grade/Course/Topic: 10-11 grades/Chemistry I Honors/Reaction Energy- exo/endothermicity and specific heat

Source of Lesson:www.watertownps.org/file/3141/view (PDF file found through search engine. Originated on http://www.watertownps.org/)

Concepts:Thermochemistry is the study of the transfers of energy as heat that accompany chemical reactions and physical changes. Heat and temperature should never be confused. Temperature is the measure of the average kinetic energy of the particles in a sample of matter, whereas heat is the energy transferred between two samples of matter of different temperatures. A reaction that gives off heat during a reaction, often resulting in an increase of temperature, is termed an exothermic reaction. On the other hand an endothermic reaction absorbs heat, resulting in a decrease in temperature of the system. The energy absorbed or released as heat in a chemical or physical change can be measured in a calorimeter. The amount of energy as heat required to raise one gram of a substance by 1 degree Celsius or Kelvin is defined as that materials specific heat, an intrinsic property of a substance. Heat transfer is often represented by the equation q=mcΔT. If you know any three of the four variables of a reaction (energy transferred in joules,q, the specific heat of a material, c, the amount used, m, and the temperature change) the fourth can be calculated. The energy transferred in a reaction is normally describes in units of joules.

Source:Davis, Raymond, Regina Fre, Mickey Sarquis, and Jerry Sarquis. Modern Chemistry. Houton Mifflin Harcourt, 2010.

Florida Sunshine State Standards

SC.912.P.10.7: Distinguish between endothermic and exothermic chemical processes. Depth of Knowledge: Moderate

SC.912.N.1.1: Define a problem based on a specific body of knowledge, for example: biology, chemistry, physics, and earth/space science, and do the following:  

5. plan investigations,6. use tools to gather, analyze, and interpret data (this includes the use of measurement in

metric and other systems, and also the generation and interpretation of graphical representations of data, including data tables and graphs),

Depth of Knowledge: High (this includes all 11 objectives under this one standard)

Performance Objectives:

Students will be able to:1. Cite evidence that supports if a reaction is endothermic or exothermic based upon a

change in temperature or heat transfer2. Calculate the amount of energy transferred in a reaction, provided the known specific

heat values of the substances involved. (specifically the energy in joules)3. Gather and analyze data to determine the substance that, when combined with

water, would be most effective for use in a chemical cold pack.

Materials List and Student Handouts:

For Demo:2 sandwich bags2 small beakers or clear plastic cupsBaking sodaVinegarLarge tray or bucket

Per student:Cold Pack Chemistry HandoutGuided notes handout

Per Pair of students:2-5 g ammonium chloride2-5 g calcium chloride2-5 g sodium chlorideThree styrofoam cupsDigital balanceVernier temperature probe Vernier Interface SystemDistilled waterScoopula50 mL graduated cylinder

Advanced Prep:Make sure PowerPoint is adaptable to school computer. Have clicker questions prepared for the end of day 2. Have all materials ready to go at stations before class begins on day 1. Have X-Men video downloaded prior to day 2.

Safety:Do not handle the salts with bare hands, especially ammonium chloride. Wear safety goggles at all times. No food, drinks, or gum at lab stations. Ammonium chloride is toxic.

Day 1

Engage Time: 5 -10 minutesWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsPre-Assessment (given the day before): All assessments in full at end of 5E

A company in Gainesville is trying to develop a new brand of cold packs. The cold packs will contain one chemical mixed with water. The company would like your help in determining which of the following chemicals is best for use in a cold pack: Ammonium Chloride, Calcium Chloride, and Sodium Chloride. The temperature change was recorded for each reaction of salt in water.

Demo an endothermic reaction of baking soda and vinegar.

Have five students come up and volunteer. Two students will each hold a sandwich bag filled with about 2-3 tablespoons of baking soda. Two students will have a beaker or container filled with about 25-50 mL of vinegar. They will pour the vinegar into the bags while the bag holders partially close the bags to keep the reaction from significantly overflowing. Have one student holding a large tray underneath the bags in case of overflow.

Introduce today’s lab:Cold packs work by mixing a chemical, usually a salt, with water to create an endothermic

What question are you trying to answer in this experiment?

What are the independent and dependent variables?

What is the difference between an exothermic and endothermic reaction? Use the terms temperature AND heat in your answer.

Hold your hand against the bag. What do you feel?

What kind of reaction is this? Endothermic or exothermic? Why?

Relate this reaction to a cold pack. What is a cold pack?

What needs to happen for a cold pack to be effective?

What salt would be the most effective chemical for use in a cold pack?

[Which salt will make the best cold pack?]

[Independent- type of saltDependent- temperature change]

[exothermic – releases heat and causes an increase in temperature; endothermic – absorbs heat and causes a decrease in temperature]

Its getting colder

Endothermic; it is getting colder, it is absorbing heat

[It needs to absorb heat, decrease in temperature, get cold, etc.]

To be answered…

reaction. Today we are going to test 3 different salts to determine which one would be the most effective for use in a cold pack.

Evaluation/Decision Point Assessment Student OutcomesPre- AssessmentIf students completely don’t understand how to identify variables and constants in an experiment they will not be able to effectively create a procedure.

Questions 3-6 are used to identify what students already know. It is expected that students are already familiar with the terms exothermic and endothermic.

Successful completion of questions 1 and 3 on pre-assessment for the majority of the class before moving onto exploration. If students do not understand this a few minutes should be taken to address the difference between independent and dependent variables and constants. Often students just need a quick reminder or explanation of what is being asked for.

In order to continue on students only need to be familiar with the terms exothermic and endothermic. This usually becomes apparent right when a question is asked about endo/exo thermicity

Explore Time: 40-45 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsHave students read the first page of the “Cold Pack Chemistry” handout. Then have students answer question 1-3 of step 1.

Put students in pairs to develop their own procedure. Make sure to go over safety concerns:Wear gogglesDo not handle chemicals with bare hands, always use the scoopula.

Read Individually and answer questions 1-3 of step 1 on the worksheet (5 min, if they don’t finish numbers 2 and 3 that is ok because the next part is going over answers as a class):

1. In your own words describe the problem you will be investigating? 2. Identify the factors that need to remain constant throughout the experiment.3. Identify the independent and dependent variables.

As a class:What is the problem we are trying to answer?

What factors must remain constant?

What is the independent variable? (the variable you will be manipulating)

What is the dependent variable? (the one that will change depending on the independent variable) Given the problem, materials list, and data tables provided, develop a procedure to answer the problem you are investigating. Keep in mind the answers you wrote to questions 1-3. When finished have teacher check your

Students should not have difficulty identifying the problem being investigated. However they may have issues identifying constants and variables if they have never had to create their own experiment.

[Which salt when mixed with water will create the best solution for a cold pack.]

[Amount of water in each trial; the same amount of each solute must be added; the method of obtaining temperature (will you stir it or not)]

[The type of solute]

[Temperature]

If students have never written their own procedures this may be difficult. However, since we have already identified the different constants and variables of the experiment, and they are given a table that tells them what type of data they will be collecting, it

Have students complete the experiment they have designed. Indicate that students will be given a set amount of water (50 mL) for each cup. Give each group a different amount of chemical to use. Write that amount on each of the three cups for each group so that there is no confusion. Each group will write the overall temperature change on the board at the end of the experiment.

procedure before moving onto the experiment.

Questions that students will answer with their partner at the end of the experiment. (On lab sheet). However, while circulating during the experiment the teacher should ask these questions to get them thinking.

Which salts gave an exothermic reaction? An endothermic reaction? How do you know this?

Which of these chemicals would make the best cold pack solution? Why?

How do you think using a larger quantity of salt would affect the change in temperature? Was your prediction correct?

After turning in their lab, go over the questions as a class.

Is that what you expected to happen? (in reference to some salts creating exothermic reactions and some creating endothermic reactions)

What were some possible factors that messed up or could have messed up your results?

How could you correct for these errors?

should not get too complicated. Students may have difficulty writing the procedure so that it could be performed easily by a different person.

[NaCl (can’t tell), CaCl2 (exothermic), NH4Cl (endothermic); determined by the change in temperature of the solution]

[Ammonium Chloride because it is the only one that decreased in temperature]

[Increasing the amount of solute will create an even larger change in the temperature.] Some students may think that the amount of solute doesn’t make a difference in the temperature change.

Answers will vary

[probe wear that wasn’t accurate, the system wasn’t closed/the cup was open at the top/not fully insulated, we used mass not moles, etc]

[use a closed cup/calorimeter, use the same number of moles instead of the same mass, etc]

Which chemical would you choose for a cold pack? Why?

Answers will vary. Some students will choose ammonium chloride since it gets the coldest, however, some students will pick sodium chloride since it gets a little bit cold, but it gradually decreases (ie last longer)

Evaluation/Decision Point Assessment Student OutcomesPost-Lab Questions:

Although students are not turning the lab in until the next day, teacher should circulate and read student answers to these questions.

Day 1 Post Assessment:

Used to see if students understood the main points of the lab. Questions were designed so that if the student participated in the lab the answers would be easily apparent.

If students are unable to accurately answer these questions, teacher should address any issues on the spot. If there are consistent issues among all students, time should be taken before the day 1 assessment to discuss any issues that arose during the lab.

If students were unable to answer these questions correctly, for the most part, time should be spent at the beginning of the next class to review the lab in depth, instead of just a brief review.

Evaluate Time: 5-10 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsHave students turn in lab sheet at the end of class with their name and their partner’s name. Look over the questions for Day 1 to see if there are any misconceptions and look over data to make sure the experiment went as planned.

Administer clicker questions for day 1 post assessment (listed at end of lesson plan)

Lab sheet questions:1. Which of these reactions were exothermic? Endothermic?

How do you know?

2. Which of these chemicals would give the best cold pack? Why?

3. How do you think changing the amount of salt used would affect the temperature change?

What effect did adding more solute have on the temperature change?

[Exothermic- Calcium ChlorideEndothermic- Ammonium Chloride]

[because of the temperature change observed]

[Ammonium chloride because the reaction caused a decrease in temperature/absorbed heat]

[It could cause a greater temperature decrease]

[the temperature decrease is even greater]

Evaluation/Decision Point Assessment Student OutcomesDay 1 Post Assessment:

Used to see if students understood the main points of the lab. Questions were designed so that if the student participated in the lab the answers would be easily apparent.

If students were unable to answer these questions correctly, for the most part, time should be spent at the beginning of the next class to review the lab in depth, instead of just a brief review.

Day 2

Engage 5 minutesWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsX-Men Mutant, Sebastian Shaw, who can absorb energy and then transform it to raw strength or re-emit the energy.

Show video clip from “X-Men First Class”

http://www.youtube.com/watch?v=-dRuwBwnmsU

Is this mutant ability allowing him to become an exothermic or endothermic reaction? Why?

How is this related to what we did yesterday?

[Both, he was able to absorb the energy, which is characteristic of an endothermic reaction. He is also able to release that energy, which is characteristic of an exothermic reaction.]

[We tested reactions to see if they absorbed or released heat, just like we were observing with X-men]

Evaluation/Decision Point Assessment Student OutcomesOral questions posed to students:

Students should be able to connect heat transfer as demonstrated in the video to traditional chemical reactions.

If students are unable to determine exo/endothermicity based upon this video, they may have problems relating heat transfer to temperature. They may be thinking that temperature change of the system is what determines exo/endothermicity.

Explain Time: 25-30 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsIntroduce Reaction Energy:Exothermic/Endothermic Reactions and Specific Heat

Review yesterday’s lab:

Yesterday we determined exo/endothermicity by the change in temperature of a solution.

Which salt did you decide would be the best for use in a cold pack? Why?

Do you think if we changed the amount used it would make a difference in how cold it got? Why?

How would you describe exothermic and endothermic reactions in terms of heat transfer?

Did all of the salts produce an endothermic reaction yesterday? Were there any observations you made that could tell you why that is?

Use PowerPoint for next section:

Does breaking bonds require energy or release energy?What about creating bonds?

Did we observe any breaking or creating bonds yesterday?

Explain that energy is released when water attaches itself to the solute. Why is water attracted to the salt?

[Ammonium Chloride because it had the largest decrease in temperature]

[yes, the more salt there is in solution there is more to react and therefore more heat would be absorbed]

[Endothermic- absorbs heatExothermic- releases heat]

[No; No because all of the reaction looked the same and all of the chemicals used were chloride salts]Students most likely will not know the answer to why

[requires energy]Most students will know that it takes energy to break a bond.[ creating bonds releases energy]

[ yes, we observed breaking bonds when the salts dissolved]

However, they may also think it takes energy to create bonds. However, this is not the case if the two ions are attracted to each other, such as in salts.

Does it take energy or give off energy for the water to pull the ions of the salt apart?

Therefore it is a balance of these two energy transfers that occur when a salt dissolves, that determines if it is exothermic or endothermic.

Which energy transfer must be greater for an exothermic reaction to occur?

Endothermic?

Relate heat transfer and temperature.

Have each student draw and ice cube melting with arrows pointing in the direction of heat transfer. Is this reaction endothermic or exothermic?

Hopefully students will recall [the positive and negative centers of charge on water (polar molecule) are attracted to the positive and negative ions of a salt molecule.] However, students may not know why this is.

Students may be confused by this because they were just told that energy is released when ions that are attracted to each other form a bond. However, it needs to be explained that these ions are already attached and there is a very strong attraction between them, since they are ionic. [Therefore it takes energy to pull them apart.]

[Energy released by hydration > energy absorbed to separate solute]

[Energy absorbed to separate solute > energy released by hydration]

[This reaction is endothermic because heat is absorbed into the ice cube to melt it.] Many students will thin that since the ice is increasing in

Go through calculations on specific heat. First guide them through a problem, then do one or two as a class.

Why?

Whats happening to the temperature though?

In the experiment what were we measuring the temperature of? Where is the heat coming from?

Specific heat:

What is the difference between temperature and heat? Can you transfer temperature? What about heat?

How can we determine how much energy was transferred as heat?

Water has a very high specific heat. How is this beneficial to life or to industry?

Calculations that are embedded in PowerPoint to be worked out on the board (If possible add these questions to a smart board file in order to write out the calculations as they go.):

When going through these calculations ask:What is the equation for specific heat?

temperature that is it an exothermic reaction. However, they need to see that temperature is just a tool we use to indicate heat transfer not to determine exo and endothermicity.

[The surroundings, not the system.] Since the thermometer is not a part of the system it can only measure the temperature of the surroundings.

Students often don’t see the difference between temperature and heat and will think they are the same thing.

[Temperature: measure of Kinetic energy, a singular value]

[Heat: measure of the amount of energy transferred between two substances at a different temperature.]

Students not expect to know this. Just an introduction to specific heat.

[Keeps our atmosphere cool; used to cool down machinery]

By asking students these questions it will give them practice in identifying the values that theare known and

What is our mass? Temperature change? Energy absorbed?Specific heat? What are we looking for in this problem?

A 4.0 g sample of glass was heated from 274 K to 314 K and absorbed 32 J of energy as heat.What is the specific heat of this type of glass?

How much energy will the same glass sample gain when it is heated from 314 K to 344 K?

Have students do this on their own then review as a class:

A 500 mL sample of water was heated and the temperature increased from 20°C to 84°C. How much energy was transferred as heat to the water? specific heat of water = 4.18 J/(g·°C)

How would we measure the energy transferred from our experiment? Is the salt the only substance absorbing or releasing heat?

unknown and help them to get used to the equation they will be using.

0.2 J/g°C

24 J

134 J

[use the specific heat of the salt to find the energy absorbed by the salt. The water is also absorbing energy in the reaction. Therefore the energy transfer for the water and the salt must be calculated and combined]

Evaluation/Decision Point Assessment Student OutcomesStudent responses:

Students are to be actively involved in helping to answer questions posed by the teacher and specific heat calculations.

Students should be able to explain exo and endothermicity based on heat transfer and based on any temperature changes they observe in their surroundings. They should also be able to correctly identify variables in a word problem and solve for any of the unknown variables I a specific heat problem. If

Ice melting drawing:

Students should be able to determine that this is an endothermic reaction based upon the direction of heat transfer.

neither of these outcomes are met and students remains confused, it is important to make sure students understand how to do the calculations and why they are doing them, in order to move onto the exploration.

If students are still confused due to the temperature change of the ice, time must be taken to clarify why this reaction is endothermic before moving onto the exploration and evaluation.

Explore Time: 10 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsHave students complete the specific heat questions given to them on the “Cold Pack Chemistry” handout

Once students finish have their groups post on the same chart from day 1 the amount of energy that was transferred for the reaction of ammonium chloride and water.

Students may work individually or with their partner from yesterday.

From your experiment yesterday, how much energy was absorbed by the reaction of ammonium chloride with water? (students are supplied with the equation for specific heat and the specific heat values of ammonium chloride and liquid water)

Did changing the amount of salt effect the amount of energy transferred?

Questions to ask while circulating:

Do we only calculate how much energy was absorbed by the ammonium chloride? Why?

What happened to the temperature change when you added even more ammonium chloride?

If you increase the value of the mass in the specific heat calculations what would happen to the amount of energy?

What would happen to the sign of the answer if the temperature increased instead of decreased? What would a negative answer mean?

Answers will vary

[Yes, the more salt the greater the energy transfer]

[No because the water is also absorbing energy and decreasing in temperature]

[the temperature change was greater]

[more energy would need to be absorbed]

[The sign of the answer would be negative. This would mean that the reaction was exothermic]

Evaluation/Decision Point Assessment Student OutcomesCirculate and observe student calculations:

Students are to calculate how much energy was transferred in their reaction.

If students are struggling, help should be given. If there are consistent issues that arise the entire class should be addressed before finishing the exploration. If there are still multiple problems, the first problem should be worked together and the second problem to be done independently. This directly related to question four in the post assessment. Students should still be given the evaluation as it is less complicated than the lab calculations and they may be able to understand how to do simpler problems. However, if students have not accomplished these calculations they cannot move onto the elaboration.

Elaborate Time: 5 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsIntroduction to enthalpyGive students the equation for the heat of fusion of ice:

ΔHf(ice) = 333.5 J/g = q(energy in joules)/ mass

Students will use the equation above to calculate the amount of ice that would be needed to absorb the same amount of energy. If the resources are available to store a large quantity of ice you may have students test this either at the end of class or the next day. There most likely will not be enough time to have students do this in the same day, however.

What is the benefit of using a chemical rather than ice?

How much ice would you need to absorb the same amount of heat as the amount of ammonium chloride you used yesterday?

Which is more effective and/or practical: an ice pack or a chemical cold pack? Why?

[you don’t need a cooler or a refrigerator so it can be transported easier, it is more practical, for the amount used, many ice packs can actually absorb more heat than ice, there is less of a mess, etc]

Answers will vary

[Since it takes way more ice to absorb the same amount of heat, the chemical cold pack would be much more effective.]

Evaluation/Decision Point Assessment Student OutcomesStudent responses:

Correct calculations and sound reasoning for all questions posed.

The elaboration is meant to be an introduction to future topics and to extend the application of what has been learned. Completion of this outcome has no bearing on learning goals for this lesson.

Evaluate Time: 5-10 minWhat the teacher will do Probing/Eliciting Questions Student Responses/

MisconceptionsClicker Questions at the end of class

For questions 1 and 2: Define each as endothermic or exothermic and write one sentence explaining why.

1. Water mixed with a small amount of potassium chloride gives a temperature decrease of 10 degrees.

2. Sodium acetate and water mix to form a crystal, causing the solution to increase in temperature by 25 degrees.

3. Melting an ice cube is what kind of process? A. exothermicB. endothermicC. neither

Why?

4. 10 grams of an unknown salt was dissolved in water. The temperature of the solution decreased from 25 K to 10 K and absorbed 30 J of heat. What is the specific heat of this unknown salt? (provide students with the specific heat equation if desired)

[endothermic- decrease in temperature]

[exothermic- increase in temperature]

[endothermic-energy/heat is required to convert solid water to liquid water]

0.2 J/g°C

Assessments:

Pre-Assessment Questions

For questions 1 and 2 read the following:

A company in Gainesville is trying to develop a new brand of cold packs. The cold packs will contain one chemical mixed with water. The company would like your help in determining which of the following chemicals is best for use in a cold pack: Ammonium Chloride, Calcium Chloride, and Sodium Chloride. The temperature change was recorded for each reaction of salt in water.

1. What question are you trying to answer in this experiment?

2. What are the independent and dependent variables?

3. Water mixed with a small amount of an unknown salt gives a temperature increase of 15 degrees. Is this process endothermic or exothermic? Explain your reasoning.

4. Adding some baking soda to vinegar, causes the solution to decrease in temperature by 10 degrees. Is this process endothermic or exothermic? Explain your reasoning.

5. Melting an ice cube is what kind of process (exothermic, endothermic, neither)? Explain your reasoning. 6. 10 grams of an unknown salt was dissolved in water. The temperature of the solution decreased from 25 K to 10 K and absorbed 30 J of heat. What is the specific heat of this unknown salt?

Equation for specific heat: c= qmΔT

Day 1 Post Assessment Questions

1. Which of the three salts resulted in an exothermic reaction when added to water?A. Ammonium ChlorideB. Calcium ChlorideC. Sodium ChlorideD. None

2. A(n) _____________ temperature indicates an endothermic reaction.A. IncreasingB. DecreasingC. Constant

3. Adding a larger amount of salt to the water would cause which of the following?

A. no difference in the temperature changeB. a smaller temperature change

C. a larger temperature change

4. What was the independent variable in your personal experiment? Do not take other groups experiments into consideration.

A. TemperatureB. Volume of waterC. The type of saltD. Mass of salt used

Day 2 Post Assessment Questions

1. Water mixed with a small amount of potassium chloride gives a temperature decrease of 10 degrees. Is this process endothermic or exothermic? Explain your reasoning.

2. Sodium acetate and water mix to form a crystal, causing the solution to increase in temperature by 25 degrees. Is this process endothermic or exothermic? Explain your reasoning.

3. Melting an ice cube is what kind of process (exothermic, endothermic, neither)? Explain your reasoning.

4. 10 grams of an unknown salt was dissolved in water. The temperature of the solution decreased from 25 K to 10 K and absorbed 30 J of heat. What is the specific heat of this unknown salt?

Equation for specific heat: c= qmΔT

Cold Pack Chemistry

Certain chemicals when dissolved in water give off heat, while others become cold. These chemicals could be used in hot and cold packs. In this laboratory we will be focusing on the

concept of cold packs, which can be used to reduce the swelling from a bruise or injury.

A company in Gainesville is trying to develop a new brand of cold packs. The cold packs will contain one chemical mixed with water. The company would like your help in determining

which of the following chemicals is best for use in a cold pack.

Ammonium Chloride (NH4Cl)Calcium Chloride (CaCl2)Sodium Chloride (NaCl)

Your Task

You and your partner will design and conduct an experiment to determine which of the three chemicals is best for use in a cold pack.

You have been provided with the following materials and equipment, it is not necessary to use all of the materials that have been provided.

0-5 g Ammonium Chloride0-5 g Calcium Chloride0-5 g Sodium Chloride4 Styrofoam cupsAccess to an electronic balanceDistilled WaterScoopula1 graduated cylinderVernier Temperature Probe system with time

Day 1Step 1:

1. In your own words, describe the problem you are going to be investigating.

2. Identify the factors that need to be held constant throughout the experiment.

3. Identify the independent (what we will be manipulating) and dependent variables (what will change depending on the independent variable).

Step 2: (Write on a separate sheet of paper. One procedure per pair is OK.)Design an experiment to solve your problem. Only use the amount of chemicals you have

been given. Your experiment should control for all variables and should be clearly described so that a stranger could easily replicate your experimental procedures.CAUTION: DO NOT MIX THE CHEMICALS TOGETHER.

Step 3:After getting approval from the teacher, work with your partner(s) to carry out the

procedure.

Data Tables

Mass (grams): Round to the nearest hundredth (ie. record 3.6492 g as 3.65 g)

Ammonium Chloride _____________ g

Calcium Chloride _____________ g

Sodium Chloride _____________ g

Temperature (°C)Initial (Before adding salt) 5 sec. 10 sec. 15 sec 20 sec 30 sec 1 min

Ammonium ChlorideCalcium ChlorideSodium Chloride

Step 4: Write your results in the chart on the board.

Questions:

1. Which of these reactions were exothermic? Endothermic?

Exothermic-

Endothermic-

How do you know?

2. Which of these chemicals would give the best cold pack? Why?

3. How do you think changing the amount of salt used would affect the temperature change? Why?

Day 2 - Calculations using specific heat:

Tinitial- same as initial temperature in your data tableTfinal- the LOWEST temperature your solution reachedΔT is the same for both numbers 1 and 2

Specific heat of NH4Cl: c = 1.572 J

g° C Specific heat of water: c = 4.184

Jg° C

1. Use the specific heat equation to find the number of joules absorbed by the water. q = the energy transferred in joules (J)m = the mass of water (remember, 1 mL H2O = 1 g H2O)ΔT = the change in temperature of the solution = (final temperature – initial temperature)

Specific heat (c) = q

mΔT

2. Use the specific heat equation to find the number of joules absorbed by ammonium chloride.q = the energy transferred in joulesm = the mass of NH4ClΔT = the change in temperature of the solution = (final temperature – initial temperature)

Specific heat (c) = q

mΔT

3. What was the total amount of energy absorbed by the solution, in joules? Where did this energy come from?