Bond Calculations

• Exothermic reaction


  Energy is transferred from the chemical to the surroundings
• Endothermic reaction


  Chemicals gain energy from the surroundings
• Calculating energy changes


  1. Look at formed energy when breaking chemical bonds

  2. Determine energy required to break bonds

  3. Determine energy released when making bonds

  4. Calculate final energy change
• Bond energy


  Energy required to break that bond
• The reaction is exothermic as the final energy change is negative
• Calculating energy change for a chemical reaction using bond energies

  1. Break bonds on left side

  2. Make bonds on right side

  3. Calculate total energy input

  4. Calculate total energy output

  5. Subtract energy output from energy input to get overall energy change
• Bond energy


  Energy required to break or make a chemical bond
• Bond breaking is endothermic (positive energy change), bond making is exothermic (negative energy change)
• The overall energy change for a reaction is calculated by subtracting the total energy of bond making from the total energy of bond breaking
• Exothermic reactions release energy, endothermic reactions absorb energy