Physical Science Name

Physical ScienceName:

Activity - Heat Mixes I

Objective:To predict and measure the final temperature of mixture of two cups of water at different original temperatures; to predict and measure the final temperature of a mixture of water and a metal with different original temperatures.

Equipment:3 Styrofoam cups

a 250-400mL beaker

a Celsius thermometer

two metal samples

a 100mL grad. cylinder

a triple beam balance

PART A: water and water

Discussion:If you mix a pail of cold water and hot water the mixture will have a final temperature between the initial temperatures of the two. What information do you need to make a prediction for the final (equilibrium) temperature? Your goal will be to investigate what happens when you mix equal masses of water at different temperatures. Imagine a cup of water at 60°C and a pail of water at 20°C...

(circle one)

1. Which do you think is hotter the cup or the pail?cuppail

2. Which do you think has more energy?cuppail

3. Which would take longer to change its temperaturecuppail

by 10°C if placed in a refrigerator?

4. If you put the same amount of molten copper in cuppail

the cup and pail, which one would change temperature

more quickly?

Procedure:1. Fill two Styrofoam cups with equal amounts of hot and cold water. Measure and record the temperature of both cups in Data Table 1A.

2. Predict the final temperature of the mixture and record your prediction in Table 1A.

3. Pour the two cups of water into a third cup (or into a beaker) and mix together. Record the final temperature of the mixture.

4. Repeat the above procedure using twice as much cold water as hot water. Record measurements in table 1B.

PART B:water and metal

Discussion:If you throw a hot metal into a pail of cold water you know that the rock will cool and the temperature of the water will rise. Will the temperature change of the water be more, less, or the same as that of the metal? Or will the temperature changes depend in some way on the amount of water and metal present?

Suppose that equal mass of water and metal are present at the same temperature. You then add the same amount of heat to each.

(circle one)

Which one would change in temperature more?metalwatersame

Procedure:1. Mass two samples of the same metal (we will use two samples b/c one may

not be enough to significantly change the temperature of water.).

2. Add the masses of the two pieces of metal. Measure out an equal mass of cold water as you measured for the metal. Put it into one of the styrofoam containers.

3. Boil enough water to fill a styrofoam container ½ full. Pour it into the empty container and put the metal in the hot water and allow a few minutes for the mixture to reach thermal equilibrium. Why?

4. Measure and record the temperature of the metal (hot water) and cold water and record in Data Table 2A.

5. Predict the final temperature--at thermal equilibrium-of the hot metal and the water.

6. Quickly lift the metal out of the hot water and place into the cold water. Allow time to reach thermal equilibrium and measure the temperature. Record this in Data Table 2A.

7. Repeat the above steps using a mass of water only half thatof the metal. Record measurements in table 2B.

Questions:1. In part 1A, how close is your prediction to the observed value? Explain in terms of mass and specific heat.

2. In part 1B which of the samples changed temperature more the hot or cold water? Explain.

3. In part 2A which of the samples had a greater change in temperature, the metal or the water? Explain in terms of mass and specific heat.

4. In each of the trials does the amount of heat lost by the warmer sample equal the amount of heat gained by the colder sample, in theory? In reality? Explain.

5. Use the conclusions drawn in this lab to explain why the climate of a mid-ocean island stays very constant?

1. Which would burn you worse, hot water at 100°C or hot metal at 100°C? Explain in terms of specific heat and energy transfer.

Error Analysis: Explain why the final temperatures of the mixtures might be a bit lower than you expected. Explain why massing the metal in part B and then using an equivalent amount of water might not be so accurate. Discuss any other sources of error in this lab.

Conclusions:What did you do? What did you find? What generalizations can you make?

Extension:Use the equations Q=mCp∆T and Ql = Qg to verify all of your findings.

Heat Mixes - Data Tables

Cp(water)=______Cp(metal)=______