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apparently only works for heat transferred reversibly. How do we know when the situation has heat transferred reversibly, and what exactly does this mean? Quite a few of the homeworks so far have used this equation but there is no specification on the method of heat transfer. I am really confused because chapter 8 was really explicit about a system expanding reversibly or at constant pressure.
If there is a heat reservoir in the surroundings, the temperature will be constant and therefore heat will be reversible. If a system is doing work, it is losing energy but heat from the surroundings can be added to the system to replace the energy lost. For instance, during a phase change, work is being done by the system to change the phase of a substance, such as from ice to liquid water. The temperature of the system does not change, yet the enthalpy does. Therefore, heat (q) must be going into the system. You should also be aware that deltaS = q/T is equivalent to nRTln(V2/V1).
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