Closed system

A closed system is a thermodynamic system , beyond the system boundaries of which no matter can pass. In contrast to the closed system, however , an exchange of energy with the environment is entirely permitted. A closed system can clearly be imagined as a tight container that is, however, deformable and has walls that are thermally conductive . The first law of thermodynamics for closed systems is:

${\displaystyle \mathrm {d} U=\delta W+\delta Q}$

In words: the change in internal energy is equal to the sum of the work added (e.g. through compression ) and heat added (e.g. through heat conduction). The second law is:

${\displaystyle \mathrm {d} S={\frac {\delta Q}{T}}+{\frac {\delta W_{\mathrm {diss.} }}{T}}}$

This means that the entropy in the closed system increases with the absorbed heat and the dissipated work.

In addition, in the context of classical physics, mass conservation applies :

${\displaystyle m=\mathrm {const.} }$

In relativistic physics , however, the decrease in the energy content of the system automatically leads to a decrease in the mass of the system (see mass-energy equivalence ).