Calculating Bond Energies

• In exothermic reactions, energy is transferred from the surroundings.
• Exothermic energy changes are shown as negative, because the energy has ben transferred from the chemicals
• In endothermic reactions, energy is gained from the surroundings.
• Endothermic energy changes are shown as positive because energy has been gained
• When we break a chemical bond, it requires energy (endothermic).
• Making bonds releases energy (exothermic)
• We need the structures of molecules involved, and the energy value for each bond
• The left hand side bonds are being broken. and the right hand side bonds are being made
• We need positive values on the left hand side
• Take away the products from the reactants.