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Thermal Energy Lab 2

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					How can you predict the final temperature of a mixture of two different temperatures of water? Hypothesis The final temperature of a mixture of water depends on and (Explain your reasoning based on personal observations and information from this class.) Materials hot water source, cold water source, two 400mL beakers, calculator, link cable, temperature probe Procedure A. Set-up of temperature probe 1. Attach the calculator to the CBL using the link cable. 2. Plug the temperature probes into Channel 1 and Channel 2 on the CBL. 3. Press the “PRGM” button on the calculator. Select “PHYSICS” as the program, and press “enter.” 4. At the main menu screen, select “1: SET UP PROBES.” 5. Enter “2: TWO” as the number of probes. 6. For type of probes, select “6:Temperature.” Confirm that the probes are in the appropriate channels. 7. At the main menu screen, select “2: Collect data.” 8. At the data collection screen, select “2: Monitor input.” From this point on, each of the temperature probes will be continuously taking temperature readings and displaying the data on your calculator screen. B. Experimental Procedure 1. In one beaker, place 50mL of hot water. In a separate beaker, place 250mL of cold water. 2. At your lab station, measure the temperature of the water in each beaker. Be sure to wait until the temperature stabilizes before recording the temperatures. 3. Mix the two volumes of water together in one beaker. Take the final temperature of the mixture. 4. Once your data is collected, pour the water down the sink. 5. Repeat the experiment with the following mixtures a. 100mL hot water, 200mL cold water b. 150mL hot water, 150mL cold water c. 200mL hot water, 100mL cold water d. 250mL hot water, 50mL cold water C. Clean up 1. Clean out and return beakers. 2. Press the “+” button on your calculators to stop data collection. Select “Return to Main Menu” from the data collection screen, then “7: Quit” from the Main Menu. 3. Unplug the temperature probes and dry them off. 4. Turn off the CBL and calculators and remove the cables. 5. Return the beakers, temperature probes, and CBLs. Keep your calculator for the conclusion section. Data Ratio of hot water: cold water 50:250 100:200 150:150 200:100 50:250 Graph the temperature of the mixture against the amount of hot water added to the mixture.

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Temperature hot water

Temperature cold water

Temperature of the mixture

Calculated value of mixture

Conclusion 1. Did all of the mixtures have the same final temperature? Did this result agree with your hypothesis?

2. 3. 4.

What two factors influence the final temperature of a mixture of water? How does the amount of hot water added to a mixture relate to the temperature of the mixture? If you graphed the temperature of your final mixture against the volume of cold water added to the mixture, how would that graph differ from the graph you made? Explain why it would differ. 5. If you need to make a mixture of water at 73 C and you only have water at 100 C and 14  C, will you use more hot water or cold water? Explain your answer. 6. Your mother makes hot cocoa by filling the cup ¾ full of boiling water, then topping the cup off with milk. Her cocoa is a temperature of 61C. You like your cocoa at 68 C. Describe how you would change your method of making hot cocoa to make sure your beverage is the appropriate temperature. 7. The relationship between temperature and volumes of a mixture of water can be expressed as T1*V1 + T2V2= TfVf. Describe this equation in words, if 1 is hot water and 2 is cold water. 8. Use the equation in question 7 to calculate the estimated temperature for each mixture in the experiment. Enter these as “calculated data” in your data table. How do these temperatures compare with the actual temperature of the mixture? Explain why there may be differences between the actual temperature of the mixture and the calculated temperature. 9. You have 28mL of hot water and 272mL of cold water. Using the temperatures from this experiment, find the temperature of the mixture according to your graph. Now, calculate the final temperature. How close was your estimate? 10. Explain at a molecular level why a larger volume of hot water will heat a mixture to a higher temperature than a smaller volume. Note: This experiment can also be carried out using thermometers instead of temperature probes.


				
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Jun Wang Jun Wang Dr
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