Bond Energies

• What are bond energies used to determine?

  Whether a reaction is exothermic or endothermic
• What does bond energy refer to?

  The energy needed to break one mole of a bond
• What is the bond energy of hydrogen chloride?

  431 kilojoules per mole
• What does a positive bond energy indicate?

  Energy must be supplied to break the bond
• Why is breaking bonds considered an endothermic process?

  It requires energy from the surroundings
• What is the nature of bond formation?

  It is an exothermic process
• In the reaction of hydrogen and chlorine, what bonds need to be broken?

  The hydrogen-hydrogen and chlorine-chlorine bonds
• How do you determine if a reaction is exothermic or endothermic?

  Compare energy required to break bonds and released
• What is the formula to calculate overall energy change?

  Energy required to break bonds minus energy released
• What is the energy required to break one hydrogen-hydrogen bond?

  436 kilojoules
• What is the energy released when forming two hydrogen chloride bonds?

  862 kilojoules
• What does a negative overall energy change indicate?

  The reaction is exothermic
• In the nitrogen and hydrogen reaction, what bonds need to be broken?

  One nitrogen-nitrogen triple bond and three hydrogen-hydrogen bonds
• What is the energy required to break one nitrogen-nitrogen bond?

  941 kilojoules
• How many nitrogen-hydrogen bonds are formed in the reaction?

  Six nitrogen-hydrogen bonds
• What is the overall energy change for the nitrogen and hydrogen reaction?

  -16 kilojoules per mole
• What does the displayed formula help visualize in a reaction?

  The bonds that need to be broken and formed
• What are the steps to determine if a reaction is exothermic or endothermic?

  1. Identify bonds that need to be broken.
  2. Calculate energy required to break those bonds.
  3. Identify bonds that will be formed.
  4. Calculate energy released by forming those bonds.
  5. Compare the total energy required and released.
• What are the key concepts of bond energies in reactions?

  • Bond energy indicates energy needed to break bonds.
  • Breaking bonds is endothermic; forming bonds is exothermic.
  • Overall energy change determines reaction type.