•Energy is required to heat substances and to produce phase changes. Phase changes require
larger amounts of energy than the amounts needed to heat the same substance as a solid, liquid, or
gas. Physical and chemical changes always involve energy transfer, either in the form of work or heat,
between a system and its surroundings.
•According to the law of conservation of energy: heat lost = heat gained
•Heat energy is measured in calories (cal) or joules (J) using a calorimeter. The joule is the SI unit of energy, although calories are