Bond Energy

• Bond Energy: The amount of energy required or released when a bond is formed or broken respectively. The unit measure of this energy is kJ/mol.

• The energy change in a reaction is calculated using the following formula:

  
  

  $\Delta H\ =$ Bond Breaking - Bond Forming
• If overall heat energy value is negative, reaction is exothermic
• If overall heat energy value is positive, reaction is endothermic
• Example of Energy Change

  $H_2\ +$$\ CL_2\ =$$\ 2HCl$

  
  

  H-H: Bond energy = 436

  CL-CL: Bond energy = 243

  H - CL: Bond energy = 432

  
  

  Bond breaking ⟶ 436 + 243 = 679 kj/mol

  Bond forming ⟶ 2 (432) = 864 kj/mol

  
  

  Thus ∆ H⟶ 676 - 864 = -185 kj/mol

  
  

  The reaction is exothermic in nature