Bond energy: energy needed to break the bond between two atoms, measured in kJ/mol, we can use bond energies to work out the energy change ('delta' H)
Here are a few bond energies (kJ/mol) for some chemical bonds:
- C-C: 347, C-O: 358, O=O: 498, C-N: 286
How to calculate Energy Change in a chemical reaction:
1) How much energy is needed to break bonds in the reactants, 2) How much energy is released when new bonds are formed in the products
3) When we want to calculate step 2, we use the same values of bond energies but put a negative sign in front of the number as the energy is being released, and the bond energy values are for when the bond is being broken (e.g bond energy for forming a C-C is -347 kJ/mol)
- Bond Breaking (in the reactants) is an endothermic process
- Bond Forming (in the products) is an exothermic process
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