The "first law of thermodynamics" is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed. It can also be stated in the following form:The energy gained (or lost) by a system is equal to the energy lost (or gained) by its surroundings.