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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.
28 Απρ 2023 · We introduce heuristic arguments to infer that \ (\Delta S=0\) is not possible for a spontaneous process in an isolated system. From this, we show that \ (\Delta S_ {universe}>0\) for any spontaneous process and hence that \ (\Delta S_ {universe}=0\) is not possible for any spontaneous process.
Entropy Changes in Reversible Processes. Suppose that the heat absorbed by the system and heat lost by the surrounding are under completely reversible conditions. In other words, qrev is the heat absorbed and lost by the surrounding at temperature T, then we can say that the entropy change in the system will be given by the following relation. (26)
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 Second Law of Thermodynamics prohibits a decrease in the entropy of a closed system and states that the entropy is unchanged during a reversible process. Then why do we say that $\Delta S = \int_a^b{\frac{dQ}{T}}$ for a reversible process?
This ratio of \(Q/T\) is defined to be the change in entropy \(\Delta S\) for a reversible process, \[\Delta S = \left(\dfrac{Q}{T} \right)_{rev},\] where \(Q\) is the heat transfer, which is positive for heat transfer into and negative for heat transfer out of, and \(T\) is the absolute temperature at which the reversible process takes place.
28 Ιουν 2019 · In a reversible process, the entropy change of the system and surroundings are equal and opposite. In an irreversible process, we generate extra entropy. We can assign that "extra" irreversible entropy either to the system or to the surroundings.
