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
• If the bond energy of hydrogen chloride is 431 kJ/mol, how much energy is needed to break one mole of these bonds?

  431 kilojoules
• Why is breaking bonds considered an endothermic process?

  It requires energy from the surroundings
• What happens during bond formation?

  Energy is released to the surroundings
• In the reaction of hydrogen and chlorine forming hydrogen chloride, what bonds need to be broken?

  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 total energy required to break one hydrogen-hydrogen bond and one chlorine-chlorine bond?

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

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

  The reaction is exothermic
• In the nitrogen and hydrogen reaction, how many nitrogen-hydrogen bonds are formed?

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

  2,330 kilojoules
• What is the energy released when forming six nitrogen-hydrogen bonds?

  2,346 kilojoules
• What is the overall energy change for the nitrogen and hydrogen reaction?

  -16 kilojoules per mole
• 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 two energy values.
• What is Avogadro's constant?

  • \(6.02 \times 10^{23}\) particles per mole
• What is the significance of a negative energy change in a reaction?

  • Indicates the reaction is exothermic
  • Energy is released to the surroundings