The first law of thermodynamics describes how the heat added to a system is conserved. heat the internal energy of the system or is transformed into , or both. heat is just transformed, not created or destroyed.

The first law of thermodynamics describes how the heat added to a system is conserved.

Explanation:

According to the first law of thermodynamics:  

"Energy is not created, nor destroyed, but it is conserved."  

Therefore, this law relates the work and the transferred heat exchanged in a system through the internal energy, which is neither created nor destroyed, it is only transformed.  

In other words: The change in the internal energy of a system is equal to the net heat that is transferred to it plus the net work done on it.