Bond Energies

• What is the focus of this page?

  It discusses bond energies in chemical reactions.
• What causes energy changes in chemical reactions?

  Making and breaking chemical bonds.
• What is required to break chemical bonds?

  • Energy must be supplied to break bonds.
  • Energy is released when new bonds form.
• What happens during a chemical reaction?

  Old bonds are broken and new bonds are formed.
• What is the role of energy in breaking bonds?

  Energy must be supplied to break existing bonds.
• What is released when new bonds are formed?

  Energy is released during bond formation.
• What is the relationship between bond breaking and energy?

  • Bond breaking requires energy input.
  • Bond formation releases energy.
• What is the bond energy for H-H?

  +436 kJ/mol
• What is the bond energy for Cl-Cl?

  +242 kJ/mol
• What is the bond energy for H-Cl?

  +431 kJ/mol
• How do you calculate the energy required to break bonds?

  Add the bond energies of the bonds broken.
• What is the total energy required to break H-H and Cl-Cl bonds?

  +678 kJ/mol
• What is the overall energy change in a reaction?

  It is the sum of energies needed to break bonds.
• What is the significance of the overall energy change?

  It indicates whether a reaction is exothermic or endothermic.
• What is the process to calculate overall energy change in a reaction?

  1. Calculate energy required to break bonds.
  2. Calculate energy released from forming bonds.
  3. Subtract the total energy of bonds formed from bonds broken.
• What is the energy change when bonds are broken compared to when they are formed?

  More energy is released when forming bonds.
• What is the bond energy associated with a chemical bond?

  It is the energy required to break that bond.
• How can you use bond energies to calculate energy changes in reactions?

  • Use known bond energies.
  • Calculate total energy for bonds broken.
  • Calculate total energy for bonds formed.
  • Determine overall energy change.
• What is the bond energy for H-H in kJ/mol?

  +436 kJ/mol
• What is the bond energy for Cl-Cl in kJ/mol?

  +242 kJ/mol
• What is the bond energy for H-Cl in kJ/mol?

  +431 kJ/mol
• What is the total energy required to break the original bonds in the reaction?

  +678 kJ/mol
• How do you determine if a reaction is exothermic or endothermic?

  By comparing energy released and energy required.
• What is the importance of practicing bond energy calculations?

  • Helps understand energy changes in reactions.
  • Essential for predicting reaction behavior.
  • Useful for various chemical applications.
• What is formed when H and Cl combine?

  HCl
• What is the bond energy required for H-H?

  436 kJ/mol
• What is the bond energy for Cl-Cl?

  242 kJ/mol
• What is the bond energy for H-Cl?

  431 kJ/mol
• How do you find the energy required to break original bonds?

  • Add the bond energies:
  • E(H-H) + E(Cl-Cl)
  • = 436 kJ/mol + 242 kJ/mol
  • = 678 kJ/mol
• How do you find the energy released by forming new bonds?

  • Multiply the bond energy of H-Cl by 2:
  • 2 × E(H-Cl)
  • = 2 × 431 kJ/mol
  • = 862 kJ/mol
• How do you calculate the overall energy change for a reaction?

  • Overall energy change = energy required to break bonds - energy released by forming bonds
  • Example:
  • = 678 kJ/mol - 862 kJ/mol
  • = -184 kJ/mol
• What is the overall energy change for the reaction?

  -184 kJ/mol
• Can you compare energy changes of reactions without knowing bond energies?

  No, you need numerical differences
• How do chlorine and bromine react with hydrogen?

  • They react similarly with hydrogen.
  • Both form hydrogen halides.
• Which bond is weaker: Br-Br or Cl-Cl?


  Br-Br
• Which bond is weaker: H-Br or H-Cl?

  H-Br
• What energy is needed to break bonds in reactions with bromine?

  Less energy is needed
• What is the significance of bond energies in reactions?

  • Determines energy changes during reactions.
  • Helps predict reaction feasibility.
• What is the bond energy for N≡N?

  941 kJ/mol
• What is the bond energy for H-H?

  436 kJ/mol