The formula of enthalpy change is

change in H = U + P*(change in V)

In space since there is no air, thus atmospheric pressure = 0 , P= 0 , Pv = 0 ,

So will H = U ?

  • $\begingroup$ Yes. Then again, every compound has a vapor pressure, so in the equilibrium (given $P=0$) they all will up and evaporate, leaving you with a pretty dull environment. $\endgroup$ – Ivan Neretin Jun 6 '18 at 13:20

Well, in principle yes, for example if you had a blob of liquid floating in empty space and wanted to consider the whole blob as a thermodynamic system.

But it may be worth mentioning that wouldn't be a typical use of thermodynamics in astrophysics. Usually you'd consider your thermodynamic system to be some small part of a larger system and the larger system would be a thermal and volume reservoir, so T and P would both be nonzero.

For example, it's common to consider the thermodynamics of stars, but what you do is consider a small packet of gas to be your system, and the rest of the star to be surroundings that establish a constant T and P for your packet.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.