The first law of thermodynamics is the conservation of energy, including the equivalence of work and energy, and about assigning an internal energy to the system. The first law of thermodynamics stat...The first law of thermodynamics is the conservation of energy, including the equivalence of work and energy, and about assigning an internal energy to the system. The first law of thermodynamics states that when an amount of heat dQ is supplied to the system and an amount of work dW is done by the system, changes are produced in the thermodynamic coordinates of the system such that dU=dQ−dW.