I have studied that are 4 thermodynamical potentials wich are useful, which are the internal energy $U$, the helmholtz function $F$, the Gibbs free energy $G$ and the enthalpy $H$:
$$dU=TdS-PdV$$ $$dH=TdS+VdP$$ $$dG=VdP-SdT$$ $$dF=-SdT-PdV$$
where, $T$ is temperature, $S$ is entropy, $V$ volume and $P$ pressure. But when do we know that these processes are conserved? For example I know (and is somehow intuitive) that in an isolated system internal energy has to be conserved. But what about the others?