• When physical or chemical changes occur, they are generally accompanied by a transfer of energy.
  • The law of conservation of energy states that energy is neither created nor destroyed.
  • During most processes, energy is exchanged between the system and the surroundings.
  • A chemical reaction or physical change is endothermic if heat is absorbed by the system from the surroundings and so the temperature of the surroundings decreases.
  • An exothermic process is negative because the system is losing heat.
  • Heat flow is measured in one of two common units: the calorie and the joule.
  • The calorie is commonly used when referring to the amount of energy contained within food.
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