Demonstration: Measuring Heat FOR THE TEACHER Summary In this demonstration students will observe what happens to the temperature of water when different volumes of hot water are added and also when copper, the same temperature as the hot water is added. Grade Level High School
Submitted by ACS High School Professional Development Team Washington, D.C.
Objectives By the end of this demonstration, students should be able to • understand the concept of specific heat capacity • understand that each substance has its own unique specific heat capacity • understand that three factors contribute to the amount of heat that is transferred when two substances are mixed: temperature, mass, and specific heat capacity. Chemistry Topics This demonstration supports students’ understanding of • Specific Heat Capacity • Properties of Matter • Temperature • Heat • Mass • Energy Transfer Time Teacher Preparation: 15 minutes Lesson: 40 minutes Materials • 3 Styrofoam coffee cups • 400 mL beaker • 20 g of copper wire coiled up • 20 mL graduated cylinder • Tap water • 2 Thermometers or temperature probes • Tongs • Heat resistant gloves Safety • Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required. • You will be using hot water and hot copper in this demonstration, so make sure you have tongs and heat resistant gloves. • Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed. American Association of Chemistry Teachers
|1-286
1
Teacher Notes • Additional background information about specific heat capacity, heat transfer, and thermal conductivity can be found in a separate document for download. Procedure 1. Label the Styrofoam cups: Cup A, Cup B and Cup C. 2. Place 100 grams of room temperature water into each cup. 3. Place 20 g of copper wire into a beaker of water, and bring the water to a boil. Cup A 4. Measure the temperature of the water in Cup A, and have the students record the temperature in the data table. 5. With another thermometer, measure the temperature of the boiling water. Record in the data table. 6. Have student guess what the final temperature will be when you mix the hot water with the room temperature water. Make sure everyone writes something. 7. Using a graduated cylinder, carefully pour 10 mL (~10 g) of hot water into Cup A, and have the students record the highest temperature using the same thermometer that you used when initially measure the room temp water. Discussion Do you think that the temperature is a measure of heat? Students may say yes or no here. So, you can have them predict what will happen if you add more hot water to the room temp water. If temperature is a measure of heat, then the temperature of the resulting mixture will be the same, regardless of the amount of water added. Cup B 8. Measure the temperature of Cup B, and have students record it in the data table. 9. Measure the temperature of the boiling water again, and have the students record it in the data table. 10. Now have the students record what the resulting temperature will be if 20 g of hot water is added to the room temperature water. 11. Carefully measure out 20 mL of the hot water and pour it into Cup B. Record the highest temperature reached. Discussion Students will notice that the temperature change is larger in Cup B, so they should agree that the amount of material also is a factor in the amount of heat that is transferred. If temperature and amount of the substances are the ONLY factors of heat, if we added 20 g of hot copper, at the same initial temperature of the boiling water, we should see the same temperature change in the cool water. If the material makes a difference, we would see a different temperature change. Cup C 12. Measure and record the temperature of the water in Cup C. 13. At this stage the copper wire has been in the boiling water for more than 20 minutes. Discussion Is the temperature of the hot copper is the same as the temperature of the boiling water. a. If they have the opportunity to work with Ice Melting Blocks, they should be able to agree that the temperature of the copper is the same as the boiling water.
American Association of Chemistry Teachers
|1-286
2
b. See the lesson plan “What Makes Something Feel Warm? Modeling Energy Transfer” to find out more information about using Ice Melting Blocks. 14. Take the temperature of the boiling water and have students record it in the data table. 15. Have the students make a prediction about the resulting temperature of the water when the copper is added. 16. Using tongs, place the copper wire into Cup C. Record the highest temperature reached. Discussion Some students will be surprised at how little change in temperature there is in Cup C. Here is a great place to introduce the idea that the material also affects the amount of heat that is transferred. This property is known as Specific Heat Capacity (C p , and is defined as the amount of energy needed to change the temperature of 1 gram of a substance 1 degree Kelvin. Clearly we have three factors contributing to the amount of heat that is transferred: temperature, mass and specific heat capacity. Here we have a wonderful place to provide the equation: q = mC p ∆T Extension Add a second metal, with a different heat capacity than copper, to the beaker of boiling water, to a fourth cup of 100 grams of water at room temperature. Aluminum wire would be a good choice. The heat capacity of copper is 0.385 J/go. The heat capacity of aluminum is 0.900 J/go. The temperature change for the water when hot aluminum is added will be more than twice as much as it was when the hot copper was added.
FOR THE STUDENT Lesson
Demonstration: Measuring Heat Learning Objectives: • understand the concept of specific heat capacity • understand that each substance has its own unique specific heat capacity • understand that three factors contribute to the amount of heat that is transferred when two substances are mixed: temperature, mass, and specific heat capacity Data Table Fill out the data table as you observe the demonstration.
American Association of Chemistry Teachers
|1-286
3
Cup A
Cup B
Cup C
Cup D (Optional)
100 g H 2 O at
100 g H 2 O at
100 g H 2 O at
100 g H 2 O at
_________oC
_________oC
_________oC
_________oC
Add 10 g Hot H 2 O at
Add 20 g Hot H 2 O at
Add 20 g Hot Cu at
Add 20 g Hot Al at
_________oC
_________oC
_________oC
_________oC
Guess: Temperature of resulting mixture
Guess: Temperature of resulting mixture
Guess: Temperature of resulting mixture
Guess: Temperature of resulting mixture
_________oC
_________oC
_________oC
_________oC
Actual Temperature of resulting mixture
Actual Temperature of resulting mixture
Actual Temperature of resulting mixture
Actual Temperature of resulting mixture
_________oC
_________oC
_________oC
_________oC
Discussion Questions Write your answers to the discussion questions. Include notes from the discussion. •
Cup A: Do you think that the temperature is a measure of heat?
•
Cup B: Is there a difference in the temperature change for the water when compared to Cup A? What factors were different that might have led to this difference?
•
Cup C: Is there a difference in the temperature change for the water when compared to Cup B? What factors were different that might have led to this difference?
American Association of Chemistry Teachers
|1-286
4
•
Cup D: Is there a difference in the temperature change for the water when compared to Cup C? What factors were different that might have led to this difference?
•
What factors contribute to the amount of heat that is transferred between two substances?
•
Define specific heat capacity.
American Association of Chemistry Teachers
|1-286
5
