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 kilojoules per mole, how much energy is needed to break one mole of these bonds?

  431 kilojoules
• What is Avogadro's constant?

  6.02 times 10 to the 23
• 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 energy
• What is the formula to calculate overall energy change?

  Energy required to break bonds minus energy released
• What is the total energy change for breaking hydrogen-hydrogen and chlorine-chlorine bonds and forming hydrogen chloride bonds?

  -184 kilojoules per mole
• What does a negative energy value indicate about a reaction?

  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 overall energy change for the nitrogen and hydrogen reaction?

  -16 kilojoules per mole
• What are the steps to calculate overall energy change in a reaction?

  1. Identify bonds to break and form.
  2. Calculate energy required to break bonds.
  3. Calculate energy released by forming bonds.
  4. Use the formula:

  • Overall energy change = Energy required - Energy released.
• What is the significance of bond energies in chemical reactions?

  • Helps predict if a reaction is exothermic or endothermic
  • Indicates energy changes during bond breaking and formation
  • Essential for understanding reaction mechanisms