Second law of thermodynamics

For a reversible change

$\left.dQ\right.=TdS$

Thus for a closed system ($n$ fixed):

$\left.dU\right.=TdS-PdV$

where $U$ is the internal energy. For an open system:

$\left.dU\right.=TdS-PdV+\mu dN$

where $\mu$ is the chemical potential.

For Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle U(S,V)} one has the following total differential

$dU=\left({\frac {\partial U}{\partial S}}\right)_{V}dS+\left({\frac {\partial U}{\partial V}}\right)_{S}dV$

See also

• H-theorem