A common signature of a chemical change is the release or absorption of energy
- The system absorbs energy: endothermic
- The system releases energy: exothermic
Energy is needed to separate a pair of bonded atoms
- The energy provided is transformed into potential energy of the separated atoms.
Heteronuclear bonds are stronger than homonuclear bonds (hydrogen is an exception H-H)
A-A + B-B → 2 A-B (weak bonds to stronger bonds = exothermic reaction = net energy release)
2 A-B-C →