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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 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.
In this page, we will see how to calculate the entropy change of an ideal gas between any two states for the most common reversible processes. The entropy change between any two states A and B is given by: Adiabatic process. An adiabatic process is a process which takes place without transfer of heat (Q = 0). Since the gas does not exchange ...
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, ...
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)
Real processes are not reversible, though, and they do change total entropy. We can, however, use hypothetical reversible processes to determine the value of entropy in real, irreversible processes. The following example illustrates this point.
Since we're talking about a reversible process, the entropy of some other system must change by an equal and opposite amount, in order to keep the total constant. That is, $\Delta S + \Delta S_\text{surroundings} = 0$.
