Entropy is not conserved
- Unlike energy functions, entropy is not conserved in natural process or in isolated systems.
- For example, consider heat transfer between two objects with different temperature TI and TII (TI > TI)in an isolated system. The two objects are connected by a thermal conductor such as a copper wire. The heat will flow from the high temperature side (I) to the low temperature side (II). Assuming no heat loss, the heat from I will go into II, thus \(Q\)\(I\)=−\(Q\)\(II\)
- The internal energy change of the whole system (I+II) is thus zero.
The energy is conserved.
- Let’s consider the entropy change of the whole system (I+II).
Insert the relation \(Q\)\(I\)=−\(Q\)\(II\)
The entropy of this isolated system is not conserved. This heat flow is spontaneous and irreversible and the irreversibility cause entropy increase.