1. Record here the patterns you see in the bond energy data from table 15.2.
Table 15.2: Average Bond Energies
Bond Energy Units used to break Energy units used to form
the bond the bond
C-H 413 required 413 required
C=O 745 required 745 required
H-O 467 required 467 required
O=O 498 required 498 required
2. Fill in the following blanks:
Bond breaking __releases______ energy
Bond formation ___requires_____ energy
Breaking a bond and forming the same bond ___requires the same amount of energy______
You will use the data from Table 15.2 to figure out the energy change that takes place when you
burn a very simple carbon-based substance (CH4). Similar changes take place when you burn
calories in food or break down sugar in cellular respiration.
CH4 + 2 O2 → CO2 + 2 H2O
Methane Oxygen Carbon dioxide Water
3. Use the following diagrams to create a model of one methane molecule and a molecule for 2
oxygen molecules. For the single bonds represented by one connected line, use a straight gray
pieces. For the double bonds in O2, use two curved gray pieces.
4. Calculate the energy change when you break apart the bonds in the reactants: One CH and
two O2. To do this:
● One by one, take apart the bonds in CH4 and O2.
● As you break (take apart) a bond, record the bond type and the energy transfer in
columns 1-3 of Table 15.3 (below)
● Add up all of the energy transfer from breaking the bonds, and record the total in the
bottom of column 2 in Table 15.3. In Column 3, record whether energy was required
(needed) or released (let go)
Table 15.3 Energy Calculations
Energy transfer when bonds of Energy transfer when bonds of
CH4+ 2 O2 are broken CH4+ 2 O2 are formed
Column 3 Column 5 Column 6
Column 1 Column 2 Required or Column 4 Energy Required or
Bond Energy units Released? Bond Units Released?
O=O 498 required O=C 745 released
O=O 498 required O=C 745 released
C-H 413 required O-H 467 released
C-H 413 required O-H 367 released
C-H 413 required
C-H 413 required
Total Energy Total Energy
from bonds from bonds
breaking: 2648 Required forming: 2424 released
Energy transfer when bonds of Energy transfer when bonds of
CH4+ 2 O2 are broken CH4+ 2 O2 are formed
Column 3 Column 5 Column 6
Column 1 Column 2 Required or Column 4 Energy Required or
Bond Energy units Released? Bond Units Released?
O-H 421 required C-H 413 released
O-H 421 required C-H 413 released
O-H 421 required C-H 413 released
C-O 748 required C-O 645 released
C-O 748 required O-H 467 released
C-O 748 required
C-H 577 required
Total Energy Total Energy
from bonds from bonds
breaking: 4084 required forming: 2351 released
END HERE DAY 1
START HERE DAY 2
5. Calculate the energy change when you form the bonds in the products (what’s being made):
One CO2 (Carbon Dioxide) and 2 H2O (Water) molecules.
● One by one, connect the bonds in the CO2 and 2 H2O as shown in the following
diagrams:
O=C=O H-O-H
Carbon dioxide Water
● As you form (make) the bond, record the bond type and the energy transfer in columns
4-6 of Table 15.3 (above)
● Add up all the energy transfer from forming the bonds and record the total in the bottom
row of column 5 in Table 15.3. In column 6, record whether the energy was required or
released.
6. Look at the total energy transfer when the bonds of CH4 and 2 O2 were broken, which you
calculated in Table 15.3.
a. What was the total energy transfer when the bonds of the reactants were broken?
b. Did breaking apart the bonds in the reactants take energy or release energy?
7. Look at the total energy transfer when the bonds of CO2 + H2O were formed, which you
calculated in Table 15.3.
a. What was the total energy transfer when the bonds of the products were formed?
2648
b. Did forming the bonds in the products take energy or release energy?
requires
8a. Overall, did the reaction take energy or release energy? Explain.
Requires because theres more energy being required than being released
8b. Can you figure out how much energy the reaction took or released? Show your thinking.
Yes, just add it together
9. What determines whether a chemical reaction, such as burning methane or cellular
respiration, releases or requires energy?
If theres more energy required or released
