Bond energy: breaking takes energy, forming releases it

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Methane has 4 C–H bonds, each taking 415 kJ/mol to break. How much energy breaks all of them in a mole of methane, Ari?

   1660 kJ
2. 2.

   Water has 2 O–H bonds, each taking 464 kJ/mol to break. How much energy breaks both in a mole of water, Bo?

   928 kJ

3. Read this first

   Average bond energies (OpenStax Table 7.2)

   bond	energy (kJ/mol)
   H–H	436
   Cl–Cl	243
   H–Cl	432
   O=O	498
   O–H	464
   C–H	415
   C=O	741
   N≡N	946
   N–H	390

4. 3.

   Using the table, which bond is the weakest, Kira?

   • O–H
   • Cl–Cl
   • H–H
5. 4.

   Using the table, how much energy breaks a mole of O=O bonds, Luz?

   • 464 kJ
   • 498 kJ
   • 243 kJ
6. 5.

   Does breaking a bond absorb energy or release it, Milo?

   • It releases energy
   • Neither
   • It absorbs energy
7. 6.

   Does forming a bond absorb energy or release it, Noah?

   • It releases energy
   • It absorbs energy
   • Neither
8. 7.

   Why is every bond energy in the table a positive number, Pia?

   • Bonds have mass
   • Breaking takes energy in
   • Forming takes energy in
9. 8.

   Bonds formed release more energy than bonds broken absorb. Is the reaction exothermic or endothermic, Ren?

   • Endothermic
   • Exothermic
   • Neither one
10. 9.

    Breaking bonds takes more energy than forming new bonds releases. Is the reaction exothermic or endothermic, Tala?

    • Neither one
    • Endothermic
    • Exothermic
11. 10.

    Which estimate of ΔH uses bond energies correctly, Zee?

    • Bonds formed − bonds broken
    • Bonds broken + bonds formed
    • Bonds broken − bonds formed