Lab 6: Heat Activity 1
Lab 6: Heat Activity 1
Supplies: Thermometer, Styrafoam cups, 2 rocks: they each need to fit entirely in cup (can’t
stick out the top, larger is better than really small, only one needs to fit in the cup at a time, you
won’t put them in together), scale, water boilers (stove and pot), towels.
Introduction:
Work is energy transfer by means of a force. Spontaneous energy transfer because of a
temperature difference is Heat. Heat is another form of energy. In an insulated system, if you put
a hot item and a cold item together, they will eventually come to thermal equilibrium – they will
be the same temperature – and the amount of heat (energy) the hot item lost will be exactly equal
to the amount of heat (energy) the cold item gained. This is another way to state the Law of
Conservation of Energy, and is also called the First Law of Thermodynamics. As we do these
activities, the room temperature will have an effect on the experiment, but if the measures are
done carefully, you should still be able to observe experimentally the Conservation of Energy –
this time it will be the conservation of heat energy.
The energy (heat) is represented by Q. The total change in heat of a substance is
DQ=mcDT where m is the mass, DT is the amount of Celsius degrees the temperature has
changed, and c is the specific heat. The amount of energy it takes to raise something one degree
Celsius is called the specific heat. The specific heat is different for each substance. You may
recall that we used the unit of Joule (J) for energy. We could do that for heat as well, but it is
actually easier in this experiment to use the unit of the calorie. The food Calorie you are familiar
with is equal to 1000 of these calories. We distinguish between the food Calorie and this calorie
by capitalizing the food Calorie. The reason we use the unit of calorie for heat energy is because
Heat Activity p. 2
it takes exactly 1 calorie to raise 1 gram of water 1 degree Celsius. And water is the main
substance we’ll be using in this activity.
Part A: Heat loss and gain of water
You’ll be pouring cold water into hot water, and calculating the change of energy of
each.
Before you begin, see if you can predict the following:
a. When combining equal amounts of hot and cold water, what would you expect the
final temperature of the mixture to be? (don’t give a number, describe where the temp
will end up) __________________________________.
b. A combination made up of a greater amount of hot water than cold water would have
a temperature such that: _______________________________________________.
Get hot and cold water from the tap. Carefully measure 75 grams of cold water into one
cup and place the thermometer into the cold water. Next, take a second cup and carefully
measure 75 grams of hot water into it. Record the temperature of the cold water in the table
below, then measure the temperature of the hot water. Try to record the temperature to the
nearest 0.1 degree. Now pour the cold water into the hot water, and record the temperature as
soon as it stops changing. Find the change of the temperature of the hot water, the change of
temperature of the cold water, and calculate the amount of heat energy (DQ) the hot water and
the cold water changed. In the first case, the hot and cold water each had an initial mass of 75 g.
Now you’ll repeat the experiment, using differing amounts of water as indicated. Fill in the table
below.
Heat Activity p. 3
Table 5.1 Data for Hot and Cold Water Mixtures
(If you don’t get exactly the indicated mass of water in your Styrafoam cup, write in the
amount you actually ended up with, and use that in your calculations.) Place Styrofoam cup on
scale, zero the scale, add water and take a reading.
Run # Mass of cold
water
(grams)
Mass of hot
water
(grams)
Initial
temperature of
cold water
Initial
temperature of
hot water
Final
temperature of
mixture
1
75 grams
75 grams
2
125 grams
75 grams
3
75 grams
125 grams
Table 5.2 Calculations (Remember: DT is change in temp, NOT the initial or final temp.)
Run Number DT of cold water DT of hot water DQ of cold water:
(mcold)(1)( DTcold)
DQ of hot water:
(mhot)(1)( DThot)
1
2
3
Why might the numbers for DQhot and DQcold differ? (It’s NOT because the masses are different)
______________________________________________________________________________
______________________________________________________________________________
Heat Activity p. 4
Part B: Finding Specific Heat of a Substance
In this activity you’ll find the specific heat of each of your rocks.
As you gather the data, enter it into Table 5.3 below.
Predict: When adding a hot mass to cold water, will the final temperature of the mixture be
closer to the initial water temperature or the initial rock temperature?________________
1. Measure temperature of boiling water (in Cheney, it’s not 100 degrees Celsius).
2. Measure ~200 grams of cold (maybe 5 or so degrees below room temp, not any colder
than that) water into one of your cups. Place the thermometer into your cold water, and
record the temperature below.
3. Dangle Rock 1 in the boiling water. After around 3 minutes, the rock will have the same
temperature as the boiling water. Grab a towel, pull the rock out of the boiling water,
QUICKLY dry it off and put it in the cold water. Record the final temperature of the
water once the temperature stops increasing.
4. Now, you’ll calculate the specific heat of your rock. You’ll use energy conservation to do
this, namely, the amount of energy the cold water gains is equal to the amount of energy
the hot mass lost. (Notice: DT of the water is not at all equal to DT of the rock)
*Think: for the following formula, would you use Tf-Ti for both DTs?
mwatercwaterDTwater= mrockcrockDTrock.
Rearrange the formula to solve for crock and enter the results into your table. Repeat Steps
2-5 to find the Specific Heat of your second rock.
Heat Activity p. 5
Show all your work for specific heat of both rocks here. Attach an additional page if
needed:
Table 5.3
Mass
(rock)
Mass
(water)
Ti of rock Ti of water T(final) Specific
heat of
rock
Units
Rock 1
Rock 2
Examine what you did and answer the following questions:
1. What were possible sources of error in your experiment?
2. Using the same equipment as you did before, what could you do to minimize the error?
v. 2021-02-08