Bond energies

• What type of energy is required to break chemical bonds?


  Energy must always be supplied
• What is the nature of bond breaking in terms of energy?

  Bond breaking is endothermic
• What is the nature of bond forming in terms of energy?

  Bond forming is exothermic
• Why is it important to practice bond energy calculations?


  To improve accuracy in determining energy changes
• How do chlorine and bromine react with hydrogen?


  They react in a similar way
• Why is less energy needed to break bonds in the reaction with bromine compared to chlorine?


  Because H-Br bonds are weaker than H-Cl bonds
• What can be concluded about the energy released when new bonds form in reactions with bromine and chlorine?


  More energy is released when new bonds form with bromine
• What is necessary to determine which reaction releases more energy?

  Knowing the exact difference in bond energies
• What is the balanced equation for the reaction of nitrogen and hydrogen to form ammonia?

  • N₂ + 3H₂ → 2NH₃
• How many marks is the question regarding the balanced equation worth?


  3 marks
• What are the key concepts related to bond energies?


  • Energy must be supplied to break bonds
  • Bond breaking is endothermic
  • Bond forming is exothermic
  • Practice is needed for bond energy calculations
• What is the main focus of the page about bond energies?


  It discusses what causes energy changes during chemical reactions.
• What must be supplied to break chemical bonds?


  Energy must be supplied to break existing bonds.
• What type of process is bond breaking considered?

  Bond breaking is considered an endothermic process.
• What happens during bond formation?


  Energy is released when new bonds are formed.
• What is the term for the process of bond formation?


  Bond formation is an exothermic process.
• How do exothermic and endothermic reactions differ in terms of energy?


  • Exothermic reactions: energy released by forming bonds > energy used to break bonds.
  • Endothermic reactions: energy used to break bonds > energy released by forming bonds.
• What is bond energy?


  Bond energy is the energy associated with a particular chemical bond.
• How does bond energy vary?


  Bond energy varies slightly depending on the compound the bond occurs in.
• What is the formula to calculate the overall energy change for a reaction?


  The overall energy change is the sum of the energies needed to break bonds minus the energy released when new bonds are formed.
• What are the steps to calculate the energy change for a reaction?


  1. Find the energy required to break the original bonds.
  2. Find the energy released by forming the new bonds.
  3. Calculate the overall energy change using the formula:

  Overall energy change = energy required to break bonds - energy released by forming bonds.
• What is the energy change for the reaction between H₂ and Cl₂ forming HCl?


  The overall energy change is $-184 \text{ kJ/mol}$.
• What are the bond energies for H–H, Cl–Cl, and H–Cl?


  H–H: +436 kJ/mol, Cl–Cl: +242 kJ/mol, H–Cl: –431 kJ/mol.
• How do the bond energies of Br–Br and H–Br compare to Cl–Cl and H–Cl?


  Br–Br bonds are weaker than Cl–Cl bonds, and H–Br bonds are weaker than H–Cl bonds.
• Why can't you determine which reaction releases more energy without knowing the exact difference in bond energy?


  Because less energy is needed to break the bonds in the reaction with bromine, but less energy is released when new bonds form.
• What is the bond energy for N≡N, H–H, and N–H?


  N≡N: +946 kJ/mol; H–H: +436 kJ/mol; N–H: –391 kJ/mol.
• What is the overall energy change for the reaction N₂ + 3H₂ → 2NH₃?


  The overall energy change can be calculated using the bond energies provided.