Units for Entropy

$\Delta S = \frac{q_{rev}}{T}$

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Eric Quach 1C
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

Units for Entropy

The units commonly used for entropy is J/K but I don't quite understand why it's like that. Is the unit supposed to show change in energy per kelvin?

Jessica Castro 2H
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

Re: Units for Entropy

Remember that change in entropy is the heat at a constant temperature (delta S = q / t). Therefore the units will be the units of heat (J) over the units of temperature (Kelvin) --> J/K. It is in Kelvins because that is the absolute temperature.

Philip Lee 1L
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am

Re: Units for Entropy

From searching online for a bit, it seems like "disorder" is supposed to be unitless. This makes sense as it is simply a measure of the number of possible microstates in a system.

Entropy and disorder are not the same thing. It is probably difficult to understand the physical meaning of entropy because entropy is just a relationship of functions that gives us a convenient state function. I believe entropy is similar to enthalpy in this sense. It's hard to say what enthalpy actually represents. By definition, enthalpy is just U + PV, but what does this really mean? It is only under special conditions where enthalpy gains more useful definitions (such as under constant pressure).

Karyn Nguyen 1K
Posts: 72
Joined: Fri Apr 06, 2018 11:04 am

Re: Units for Entropy

Do we have to convert C to K or can we just leave it as C?

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