The first law of thermodynamics states that

The first law of thermodynamics states that energy is not created, nor destroyed, but conserved. Then this law expresses that, when a system is subjected to a thermodynamic cycle, the heat ceded by the system will be equal to the work received by it, and vice versa.

Explanation:

The first law of thermodynamics is a version of the law of conservation of energy. Also known as the Joule Principle, this postulate admits that various forms of work can be converted into each other, elucidating that the total energy transferred to a system is equal to the variation of its internal energy, that is, in every natural process, energy of the universe is conserved and the energy of the system when isolated is constant. We also observe the equivalence between work and heat, where it was found that the Q - W variation is the same for all thermodynamic processes.