4.1a Energy can exist in different forms, such as chemical, electrical, electromagnetic,
heat, mechanical, nuclear.
4.1b Chemical and physical changes can be exothermic or endothermic.
4.1c Energy released or absorbed during a chemical reaction can be represented by a
potential energy diagram.
4.1d Energy released or absorbed during a chemical reaction (heat of reaction) is equal
to the difference between the potential energy of the products and potential energy of