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Experiment 2: Cold Packs vs. Hand Warmers In this experiment, you will observe the kinetic energy of molecules by comparing the temperature changes...

Experiment 2: Cold Packs vs. Hand Warmers

In this experiment, you will observe the kinetic energy of molecules by comparing the temperature changes in a calorimeter. Specifically, you will observe the temperature changes for cold packs and hand warmers. Since temperature is defined as the average kinetic energy of the molecules, changes in temperature indicate changes in energy. You will use a Styrofoam® cup as a calorimeter to capture the energy. The customary lid will not be placed on the cup, since ample oxygen from the air is needed for the hand warmer ingredients to react within a reasonable amount of time.



Procedure

Part 1: Cold Pack

1.   Put on your safety glasses and gloves (provided in your safety box).

2.   Measure 10 mL of distilled water into a 10 mL graduated cylinder.

3.   Turn on the scale by pressing the button labeled "0/T."

4.   Place the weigh boat on the scale and press the 0/T button a second time to zero the scale. Make sure that the units are in grams (g). If not, press the M button until the units displayed are in grams. 

5.   Using your scissors, cut off the top of your cold pack and weigh out 10 g of the ammonium nitrate (NH4NO3) crystals found in the inner contents of the pack.

6.   Place the 10 g of the ammonium nitrate into a Styrofoam® cup. The Styrofoam® cup will be used as a calorimeter.

7.   Place a thermometer and a stir rod into the calorimeter (Styrofoam® cup).

8.   Pour the 10 mL of distilled water into the calorimeter containing the ammonium nitrate (NH4NO3) taken from the cold pack.

9.   Immediately record the temperature and time in Table 4.

10. Quickly begin stirring the contents in the calorimeter.

11. Use your stopwatch or timer to record the temperature at 30 second intervals in Table 4. You will need to stir the reaction the entire time you are recording data.

12. Collect data for at least five minutes, or until the temperature reaches its minimum and begins to rise. This should take approximately five to seven minutes.

13. Record the overall minimum temperature in the appropriate place in Table 4.


Part 2: Hand Warmer


1.   The iron within the hand warmer mixes with the oxygen in the air and oxidizes in a process known as an oxidation reaction:

2.   Wash the thermometer and dry it with paper towels. Remember to rinse it with distilled water before drying. Carefully place the thermometer in the other Styrofoam® cup.

3.   Cut open the inner package of the hand warmer and quickly transfer all of its contents into the calorimeter.

4.   Immediately record the initial temperature of the contents and begin timing the reaction.

Hint: Data collection should start quickly after the package is opened, because the reaction will be activated as soon as it is exposed to air.

5.   Begin stirring the contents in the calorimeter with your thermometer.

6.   Continue stirring, recording the temperature at thirty second intervals in Table 5. You will need to stir the reaction at a consistent rate the entire time you are recording data.

7.   Set a stopwatch or timer for five minutes. Let the reaction continue for at least five minutes, or until the temperature has reached its maximum and then fallen a few degrees. This should take approximately 5 to 7 minutes.

8.   Record the overall maximum temperature in the appropriate place in data Table 5.



Table 4: Cold Pack Data

time temperature

initial 25

30 10

60 0.9

90 0.7

120 0.7

150 0.7

180 0.7

210 0.8

240 0.9

270 0.9

300 10

330 11

360 11

390 12

420 12

450 12

Time 201(

sec)



Table 5: Hand Warmer Data

time temperature

initial 27

30 40

60 47

90 54

120 59

150 64

180 67

210 69

240 71

270 71

300 70

330 69

360 69

390 69

420 69

450 69


Time (sec)

Temperature (°C)

Post-Lab Questions


2.   Calculate the overall temperature change for the cold pack (Tmax - Tmin). Show your work.

3.   Calculate the overall temperature change for the hot pack. Show your work.

4.   Which pack works by an exothermic process? Use experimental data to support your answer.

5.   Which pack works by an endothermic process? Use experimental data to support your answer.

6.   Write the balanced reaction between ammonium nitrate and water.

7.   Which pack had the greatest change in enthalpy? How do you know?

8.   Describe what would happen to the maximum temperature if the experiment used double the amount of hand warmers. Justify your answer.

9.   Describe if and how the rate of temperature change would be affected if you crushed the cold pack crystals.

10. Explain how the law of conservation of energy was observed in this experiment.

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