Chapter 6, Problem 6.29QP

Thermal Interactions

Part 1: In an insulated container, you mix 200. g of water at 80°C with 100. g of water at 20°C. After mixing, the temperature of the water is 60°C.

1. a How much did the temperature of the hot water change? How much did the temperature of the cold water change? Compare the magnitudes (positive values) of these changes.
2. b During the mixing, how did the heat transfer occur: from hot water to cold, or from cold water to hot?
3. c What quantity of heat was transferred from one sample to the other?
4. d How does the quantity of heat transferred to or from the hot-water sample compare with the quantity of heat transferred to or from the cold-water sample?
5. e Knowing these relative quantities of heat, why is the temperature change of the cold water greater than the magnitude of the temperature change of the hot water.
6. f A sample of hot water is mixed with a sample of cold water that has twice its mass. Predict the temperature change of each of the samples.
7. g You mix two samples of water, and one increases by 20°C, while the other drops by 60°C. Which of the samples has less mass? How do the masses of the two water samples compare?
8. h A 7-g sample of hot water is mixed with a 3-g sample of cold water. How do the temperature changes of the two water samples compare?

Part 2: A sample of water is heated from 10°C to 50°C. Can you calculate the amount of heat added to the water sample that caused this temperature change? If not, what information do you need to perform this calculation?

Part 3: Two samples of water are heated from 20°C to 60°C. One of the samples requires twice as much heat to bring about this temperature change as the other. How do the masses of the two water samples compare? Explain your reasoning.