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
• What does it mean if breaking bonds is 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?

  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 energy
• What is the formula to calculate overall energy change?

  Energy required to break bonds minus energy released
• 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 does it mean if a reaction has an overall energy change of -16 kJ/mol?

  It is an exothermic reaction
• What are the steps to determine if a reaction is exothermic or endothermic?

  1. Identify bonds broken and formed.
  2. Calculate energy required to break bonds.
  3. Calculate energy released by forming bonds.
  4. Use the formula: Energy change = Energy required - Energy released.
  5. Analyze the result: negative = exothermic, positive = endothermic.
• What is Avogadro's constant?

  • \(6.02 \times 10^{23}\) particles per mole
• What is the significance of bond energies in chemical reactions?

  • Helps predict reaction heat changes
  • Indicates energy absorbed or released