My introductory text book on thermodynamics has just one ambiguous mention of something like "Isochoric expansion of an ideal gas " . But does it really make sense ? Or is it just a blunder ?

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    $\begingroup$ It doesn't make sense. Isochoric process doesn't have volume change. Expansion has the volume increased. $\endgroup$
    – user115350
    Feb 1, 2017 at 20:56
  • $\begingroup$ I'm voting to close this question as off-topic because this is a question about a possible editing error in a textbook, not a question about a physical concept or principle. $\endgroup$ Feb 1, 2017 at 22:03
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    $\begingroup$ @sammygerbil: Seriously? This type of question is one of the reasons for this site: clearing up confusions about physics. $\endgroup$
    – Kyle Kanos
    Feb 2, 2017 at 9:53
  • $\begingroup$ @KyleKanos : Yes, seriously. The OP is clearly not confused about physics and is merely pointing out an isolated "blunder" in an unidentified textbook. I don't think the purpose of this site is to point out editing errors in textbooks. $\endgroup$ Feb 2, 2017 at 17:24
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    $\begingroup$ @KyleKanos : The highest voted answer in that post opens : "It depends. Generally speaking, yes, you can ask about what you think is an error in a book (or paper), but make sure you're asking an actual answerable question, rather than just looking for people to agree with you." I claim that the OP here is doing the latter. $\endgroup$ Feb 2, 2017 at 18:09

2 Answers 2


In his lectures on thermodynamics, Fermi defines an isochoric transformation as one in which the system doesn't do any external work. In this sense, the free expansion of a perfect gas (AKA Joule expansion) is an isochoric process.

However, I must say that that's the only place where I've seen an "isochoric process" defined in this way, the common definition is the one given by annav, so it might as well be just a blunder.


An isochoric process, also called a constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition

You should give more of the context where you found the quote. It might mean a "uniform expansion of volume". I found it here "expansion and compression of gas" so it might be describing an instant in an expansion.

  • $\begingroup$ Please could you be more specific about your reference to the Homework Solutions document - it has 11 pages. $\endgroup$ Feb 2, 2017 at 17:16
  • $\begingroup$ @sammygerbil search for "isochoric" in the document. I give it as a possibility of how "expansion" and "isochoric" can be found in the same page, as the OP does not give really a context. $\endgroup$
    – anna v
    Feb 2, 2017 at 17:34
  • $\begingroup$ Well I did as you suggest. I found 6 instances of "isochoric" but I don't think any of them can be interpreted as anything other than $\Delta V = 0$. I found no instances of "expansion and compression of gas" nor "uniform expansion of volume". Sorry to be pedantic but I don't understand the point you are trying to make with this reference. The co-existence of the words "isochoric" and "expansion/compression" in the same document does not prove anything. $\endgroup$ Feb 2, 2017 at 18:03
  • $\begingroup$ @sammygerbil the question is about the association , "isochoric expansion of an ideal gas" and I am trying to make the OP give the context, maybe it is similar to this. Maybe he /she found it in a similar document" . The "univorm expansion" I am talking about is similar to the one the chosen answer says: a large volume, a guess, and a gas expanding within it. $\endgroup$
    – anna v
    Feb 2, 2017 at 18:19

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