I thought boiling of water would be an isobaric process, because pressure becomes constant. However, I'm not sure about it as the 1st law of Thermodynamics is only applicable in an enclosed system. Are both boiling and freezing of water isobaric processes? Please provide reasonings, and if they aren't isobaric, then do give an example of an isobaric process. Any help would be appreciated.
5
-
$\begingroup$ You can model a phase change (such as boiling or freezing) as occurring isobarically, but you don't have to. What are you ultimately trying to achieve? It's not really clear from your question. $\endgroup$– ChemomechanicsCommented May 8, 2022 at 18:19
-
$\begingroup$ I'm just looking for examples of the 4 processes (Isothermal, Adiabatic, Isochoric, and Isobaric), but I couldn't get any correct answer. Some say freezing is isobaric, while some say it is isothermal. I'm just looking for clarification to see if I'm right or wrong. $\endgroup$– AsadCommented May 8, 2022 at 18:47
-
$\begingroup$ The classifications aren't exclusive; a phase change can be modeled as being both isobaric and isothermal simultaneously. Consider an open puddle of water (i.e., exposed to atmospheric pressure) freezing at a near-constant 0°C. $\endgroup$– ChemomechanicsCommented May 8, 2022 at 19:33
-
$\begingroup$ Are you implying that both boiling and freezing can be isothermal and isobaric at the same point? $\endgroup$– AsadCommented May 8, 2022 at 20:30
-
$\begingroup$ Yes, we can hold T and P fixed, or model them as constant. $\endgroup$– ChemomechanicsCommented May 9, 2022 at 15:46
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
2
For an enclosed system, we can thik of a vertical cylinder full of water with a top piston. Heat slowly until the boiling point. Then keep providing heat while the gas phase forms. The boiling temperature is constant, and also the pressure, because the piston is supposed free to move upward. The entropy and volume changes.
answered May 8, 2022 at 19:57
-
$\begingroup$ First of all, in my case (book and what my teacher taught me), the vertical cylinder is filled with gas, instead of water (if that makes any difference). Second of all, are you implying that boiling of water is both isothermal and isobaric? $\endgroup$– AsadCommented May 8, 2022 at 20:28
-
$\begingroup$ With this arrangement, yes. $\endgroup$ Commented May 8, 2022 at 20:38