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

the reactants.