Name: Per: Date:
Chemistry in Context 2009-10
Purpose: to analyze the energy transfer between different substances.
Procedure and Questions
1.
Go to the following website shown below. Your teacher may have a link on a school web page, or you can find it with the Google search terms “thermoequiv.swf” and Greenbowe. http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/thermoEquiv.html
2.
This animation simulates the energy transfer between metals at different temperatures. All the metal blocks are the same mass, 100 g, but they are made of either aluminum, copper, or lead. You can adjust the temperature of the metal blocks from 25°C to 200°C.
When you click start, the blocks will come into contact, and energy will be transferred until thermal equilibrium is reached. Try a few combinations before you conduct the guided experiment.
3.
Experiment 1. Click the buttons to make both blocks
Aluminum. Set the temperature of Block 1 at 200°C and that of Block 2 at 100°C.
Before you bring the blocks into contact, predict the final temperature of the two blocks. Explain your thinking.
4.
Click Start. When the temperatures have stabilized, record the final temperature. Did the final temperature match what you predicted?
5.
Experiment 2. Now keep block 1 as Al , but switch Block 2 to Cu . Set the initial temperature of Block 1 to 200°C, and that of Block 2 to 100°C. Before you bring the blocks into contact, predict the final temperature of the two blocks. Explain your thinking.
6.
Is the final temperature in Experiment 2 different from your prediction?
All the energy lost by Block 1 (Cu) was transferred to Block 2 (Al). For a given amount of energy, the block with a larger change in temperature is easier to heat up and cool down. Which block had a larger change in temperature in Experiment 2?
7.
Complete Experiments 3-4 and record the final temperature in each.
1

Table 1. Data
Exp
Block 1 (hotter)
Metal T initial
, °C T final
, °C
1
2
3
Al
Al
Cu
200°C
200°C
200°C

T =
T final
-T initial
Block 2 (colder)
Metal T initial
, °C T final
, °C

T =
T final
-T initial
Al 100°C
Cu
100°C
Al 100°C
4 Cu
200°C
Pb
100°C
Remember that a calorie is a unit of energy; specifically, it is the amount of energy needed to raise the temperature of 1 g of water 1 °C. More generally, the specific heat capacity, C , of a substance is the amount of energy needed to raise the temperature of 1 g of that substance by 1 °C. The specific heat capacities of a few substances are listed in the table.
Specific heat
8.
Judging from the table of specific heat capacity, between Al
Substance capacity, C and Cu, which metal requires less energy to raise the temperature of 1 g of the substance 1°C? water, H
2
O 1.00 cal/g °C aluminum, Al 0.217 cal/g °C copper, Cu 0.093 cal/g °C
The following equation is used to calculate the amount of energy lead, Pb
0.031 cal/g °C transferred between objects:
q = m

C
 
T where q is the amount of energy transferred, m is the mass of the material, and C is the specific heat of the material, and

T = T final
- T initial
is the change in temperature. Note that

T can be either positive or negative.
9.
In your computer experiment, when the hot block was brought into contact with the cold block, energy was transferred. Using the specific heat capacities in the table above, complete the following table, showing the amount of heat, q , transferred to or from each metal block.
Table 2.
Calculations of Heat Transferred
Exp
q = m C

T, heat transferred from Block 1
q = m C

T, heat transferred to Block 2
1 (100 g) (0.217 cal/g °C) (-50°C) = -1085 cal (100 g) (0.217 cal/g °C) (50°C) = 1085 cal
2
3
4
2

10.
In each experiment, Block 1 was the hotter block which cooled off when brought into contact with Block 2.
When heat is transferred to an object, the sign of q is _________________________(positive / negative)?
When heat is transferred from an object, the sign of q is _______________________.
11.
In Table 2, compare the amount of heat energy that left Block 1 and compare it to the amount of heat energy received by Block 2. a.
How do the amounts compare? b.
Was any heat energy lost to the surroundings? How do you know?
12.
In Experiment 2, the same amount of heat energy was transferred from the aluminum block as was gained by the copper block. Which block underwent a larger change in temperature? Is this consistent with the specific heat capacity of the metals? Explain.
13.
Use the equation q = m C

T to calculate how many calories of energy are needed to raise the temperature of 24 g of copper 45°C. SHOW YOUR WORK.
14.
Imagine that you transfer 5 calories of energy to 1 g of water and to 1 g of copper. Which sample will be at a higher temperature? Explain your thinking.
15.
Imagine that you place an aluminum pot filled with water on the stove. After several minutes, the metal is too hot to touch, but the water is barely warm. Use specific heat capacity to explain why.
3