Ok, suppose it is a hot afternoon in early May and you decide to go for a swim. Why is the
water cold?
Let’s Explore this phenomenon. Please record your work and notes on your own page.
Mixing hot things with cool things in the Calorimeter
In this activity, you will use the Gizmo™ to explore what happens when hot objects are added to cool water in the
calorimeter. How will their temperatures change after they are mixed?
1.
Make a table in your notebook to record your observations. You will need to record the substance, its mass,
its initial temperature and its final temperature. Your table should include a row for water, copper, lead and
granite.
2.
On the SIMULATION pane, select Copper. Use the sliders to set the Copper Mass to 200 g and the Water Mass
to 200 g. (To quickly set a slider to a certain value, type the number in the field to the right of the slider and
hit Enter.) Check that the Water temp is set to 30° C and the Copper temp is set to 90° C. Record the starting
values for copper in your data table.
Select the GRAPH tab. Click Play (
) to start the simulation. When the simulation ends, record the Final
temperature of the copper and the Final temperature of the water.
Take a snapshot of your graph by clicking the little camera icon in the corner (see image and arrow below).
Then paste it in a word document.
3.
4.
Answer these questions on your own page:
5.
What happens to the temperature of the copper over time?
6.
What happens to the temperature of the water over time?
7.
How do the final temperatures of copper and water compare?
8.
How much did the temperature of the copper change? How much did the temperature of the water change?
9.
Specific heat capacity can be described as a substance's resistance to temperature changes. Based on your
observations, which substance has a greater specific heat capacity, copper or water? Explain your answer.
10. Use your observations to explain why the water in a swimming pool feels colder than the air on a warm
spring day. (Hint: which substance do you think has a higher specific heat capacity, water or air?)
11. Now try changing the initial mass and temperature of the water and copper. For each experiment, record the
initial conditions and final temperature of the copper and water in your data table. Again, take snapshots as
you go so you can reference them. You may want to title your snapshots in a way that you can keep track of
them. Answer the following questions:
12. If everything else is held constant, what is the effect of increasing the water mass on the final
temperature of the system?
13. If everything else is held constant, what is the effect of decreasing the copper mass on the final
temperature?
14. What is the effect of increasing the copper temperature on the final temperature of the system?
Decreasing the copper temperature?
15. Try two experiments in which the starting copper temperature is 50° higher than the water temperature
(and all other variables are held constant). Is the amount of water temperature change the same in each
case?
16. Try two experiments in which the water mass is 4 times the copper mass. Is the amount of water
temperature change the same in each case?
Now repeat the above processes for the other substances. Make sure to deselect the copper and change to
the other substances. Adjust the starting conditions so they are the same as in the copper trial. Take
snapshots and label them so you can compare your graphs later.
Analyzing your data and graphs, think then answer these questions:
In each trial, how can you tell which substance gains energy and which loses energy?
What substance has the highest specific heat capacity?
What evidence do you have?
What would happen if the initial temperature of the water was hot and the initial temperature of the other object
was cold?
Would this affect the specific heat capacity of each substance?
Specific Heat Calculations
Because they eliminate heat loss to the atmosphere, calorimeters make specific heat calculations easier. The
specific heat equation is:
q = mc T where q = heat energy (in Joules), m = mass of the substance (in grams), c = specific heat capacity of
the substance (in J / g °C), and T= temperature change of the substance (in °C), always found by subtracting
the initial temperature (ti) from the final temperature (tf), or tf − ti.
Water is normally used as one substance in the calorimeter since its specific heat capacity is known (4.184 J / g
°C).
If you mix two substances, the heat gained by the first substance, q1, is equal to the heat lost by the second
substance, −q2. (The heat value of one of the substances is negative because it lost heat.) This allows you to set up
the following equation:
q1 = −q2,
OR
q1 + q2 = 0
Substitute the q terms and rewrite in terms of mass, specific heat capacity and change in temperature.
1.
2.
3.
4.
Use the Gizmo to mix 200 g of copper at 100°C with 1,000 g of water at 20°C. Press Play and record the final
temperature.
a.
Calculate the temperature change (tf − ti) for each substance.
b.
Plug the following known values into the last equation: The water mass (m2) is 1,000 g, and the specific
heat capacity of water (c2) is 4.184 J / g °C.
c.
Now solve for the unknown variable, the specific heat of copper (c1). SHOW WORK on your own paper
d.
Is your answer close to the accepted value in the table below? (Note: There may be small rounding errors.)
Find the specific heat capacity for granite, lead and ice and compare to the values in the table above. SHOW
WORK on your own paper.
What if we put all of the substances together instead of just two? What do you think would change about the
equation used?
Run a trial in which you have more than two substances and test your adjusted equation to see if it worked.
Use the specific heat capacities from the data table provided. Hint: set up q1 + q2 + q3 + q4 = 0 Solve for
the final temperature and compare to the trial results. SHOW WORK on your own paper.