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13 Μαΐ 2023 · Changes in entropy (ΔS Δ S), together with changes in enthalpy (ΔH Δ H), enable us to predict in which direction a chemical or physical change will occur spontaneously. Before discussing how to do so, however, we must understand the difference between a reversible process and an irreversible one.
Change in Entropy: When a system goes from state one to state two, its entropy changes by the same amount ΔS, whether a hypothetical reversible path is followed or a real irreversible path is taken. Example
28 Απρ 2023 · Since the change is reversible, the portion of the surroundings that exchanges heat with the system is at the same temperature as the system: \ (T=\hat {T}\). From \ (q^ {rev}=- \hat {q}^ {rev}\) and the definition, \ (dS=dq^ {rev}/T\), the entropy changes are. \ [\Delta S= {q^ {rev}}/ {T} \nonumber \] and.
Rearranging terms yields \[\dfrac{Q_c}{T_c} = \dfrac{Q_h}{T_h}\] for any reversible process. \(Q_c\) and \(Q_h\) are absolute values of the heat transfer at temperatures \(T_c\) and \(T_h\), respectively. This ratio of \(Q/T\) is defined to be the change in entropy \(\Delta S\) for a reversible process, \[\Delta S = \left(\dfrac{Q}{T} \right ...
Entropy transfer accompanies heat transfer. In a reversible system this enables us to calculate the change in entropy using the definition of entropy: dS = (δQ T)reversible. where δQ is the differential amount of heat exchanged in a reversible process and T the temperature of the system boundary.
For reversible processes (the most efficient processes possible), the net change in entropy in the universe (system + surroundings) is zero. Phenomena that introduce irreversibility and inefficiency are: friction, heat transfer across finite temperature differences, free expansion, ...
The infinitesimal change of entropy in a reversible process can thus be written as \[dS=\left(\dfrac{\delta Q}{T}\right)_{rev}\] where is the entropy and is the absolute temperature.
