CHAPTER INVESTIGATION
Energy Conversions
OVERVIEW AND PURPOSE All foods contain stored
chemical energy, but some foods contain more chemical energy
than others. People need this chemical energy for all of their
activities. The amount of chemical energy stored in foods like
marshmallows can be measured by burning the foods. In this
investigation, you will
• construct an apparatus to investigate the amount of
energy in samples of food
• calculate the amount of energy released when the
foods are burned
Problem
Write
It Up
How much energy is stored in different types of food?
MATERIALS
• can opener
• empty aluminum can
• dowel rod
• water
• graduated cylinder
• ring stand with ring
• thermometer
• aluminum pie plate
• aluminum foil
• tape
• large paper clip
• cork
• modeling clay
• crouton
• caramel rice cake
• balance
• wooden matches
Hypothesize
Write
It Up
Write a hypothesis to explain which type of food contains a
greater amount of chemical energy. Your hypothesis should take
the form of an “If . . . , then . . . , because . . .” statement.
Procedure
Create a data table similar to the one shown on the sample
notebook page.
Using the can opener, punch two holes directly opposite each
other near the top of the can. Slide the dowel rod through the
holes as shown in the photograph to the left.
Measure 50 mL of water with a graduated cylinder, and pour the
water into the can. Record the mass of the water. (Hint: 1 mL of
water = 1 gram)
Rest the ends of the dowel rod on the ring in the ring stand to
hold the can in the air. Carefully place the thermometer in the
can. Measure and record the initial temperature (T1) of the water
in the can.
Make a collar of aluminum foil and tape
it around the can as shown. Leave
enough room to insert the burner
platform and food sample.
124 Unit 1: Matter and Energy
Construct the burner
platform as follows:
Open up the paper
step 6
clip. Push the straightened end into a cork,
and push the bottom
of the cork into the
clay. Push the burner
onto the pie plate so it will
not move. Put the pie plate
under the ring.
It Up
1. INTERPRET Answer the question posed in
the problem.
2. INFER Did your results support your
hypothesis? Explain.
3. EVALUATE What happens to any energy
released by the burning food that is not captured by the water? How could you change
the setup for a more accurate measurement?
Find and record the mass of the crouton. Place
the crouton on the flattened end of the burner
platform. Adjust the height of the ring so the bottom of the can is about 4 cm above the crouton.
Use a match to ignite the crouton. Allow the
crouton to burn completely. Measure and record
the final temperature (T2) of the water.
Empty the water from the can and repeat steps
3–8 with a caramel rice cake. The mass of the
rice cake should equal the mass of the crouton.
Observe and Analyze
Write
Conclude
Write
It Up
1. RECORD OBSERVATIONS Make sure
to record all measurements in the data table.
4. APPLY Find out how much fat and carbohydrate the different foods contain. Explain
the relationship between this information and
the number of calories in the foods.
INVESTIGATE Further
CHALLENGE The Calories listed in foods are
equal to 1000 calories (1 kilocalorie). Calculate the
amount of energy in your food samples in terms
of Calories per gram of food (Calories/g). Using
a balance, find the mass of any ash that remains
after burning the food. Subtract that mass from
the original mass of the sample to calculate mass
burned. Divide total calories by mass burned,
then divide that value by 1000 to find Calories/g.
Compare your results to those given on the
product labels.
2. CALCULATE Find the energy released
from the food samples by following the next
two steps.
Calculate and record the change in
temperature.
change in temperature = T2 – T1
Calculate and record the energy released in
calories. One calorie is the energy needed
to raise the temperature of 1 g of water
by 1°C.
energy released = (mass of water p
change in temperature p 1 cal/g°C)
3. GRAPH Make a bar graph showing the
number of calories in each food sample.
Which type of food contains a greater
amount of chemical energy?
ions
Energy Convers
ored in
uch energy is st
Problem How m
food?
different types of
Hypothesize
nalyze
Observe and A
in Food
Table 1. Energy
ple 2
Sample 1 Sam
)
Mass of water (g
(T1) (°C)
p.
Initial water tem
p. (T2) (°C)
Final water tem
)
Mass of food (g
(T2 - T1) (°C)
Change in temp.
Energy released mp.p cal/g˚C)
te
(mass pchange in
Conclude
Chapter 4: Energy 125