Do liquid water and water vapor count as different types of matter? How does Second law of Thermodynamics apply when I pump water vapor into liquid water?
What would happen when water vapor goes into liquid water? What would I need to do to make that happen?


closed as unclear what you're asking by CuriousOne, ACuriousMind, Kyle Kanos, John Rennie, Norbert Schuch Mar 13 '16 at 21:24

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    $\begingroup$ Water vapor is a phase of water, so is liquid water. The second law says that heat will flow from hot to cold unless something else happens... so, yes, it applies. Why would it not. What happens depends on the temperatures and pressures of the two phases. $\endgroup$ – CuriousOne Mar 13 '16 at 1:12

When water vapor condenses to liquid water energy is released, about 41 kJ/mole. You need to get rid of that energy somehow. The entropy of the water is decreased, so something must have its entropy increase to compensate. When you say pump water vapor into liquid water are you just running bubbles through liquid water or applying enough pressure to cause the water vapor to condense?

  • $\begingroup$ I'm not talking about condensing the vapor. So you mean the vapor will just bubble through the liquid? $\endgroup$ – Hai Thanh Nguyen Mar 13 '16 at 1:34
  • $\begingroup$ @HaiThanhNguyen: If both have the same temperature and vapor pressure, yes. If not, then the bubble can expand or collapse. You can do both in the kitchen... people burn themselves often enough by exploding bubbles that nucleate in superheated water and then keep growing until they throw out large amounts of boiling water. You want to enter the Darwin awards? Try boiling clean water in a clean glass in the microwave and open the door at the wrong time... $\endgroup$ – CuriousOne Mar 13 '16 at 1:39
  • $\begingroup$ @CuriousOne: When does it expand, when does it collapse? And why? Do you know of any docs that I can read about this interaction? I can't find anywhere. $\endgroup$ – Hai Thanh Nguyen Mar 13 '16 at 1:48
  • $\begingroup$ @HaiThanhNguyen: Look at the phase diagram: d32ogoqmya1dw8.cloudfront.net/images/research_education/… $\endgroup$ – CuriousOne Mar 13 '16 at 1:56
  • $\begingroup$ The usual way to make pure water vapor is to boil water. That gives water vapor at 1 atm pressure and 100C temperature. If you bubble that through room temperature water, the heat will go into the liquid water and much of the water vapor will condense as the vapor pressure of water at room temperature is much lower than 1 atm. When you see bubbles going through water, say in a fish tank, they are mostly air with (maybe) an equilibrium concentration of water vapor. $\endgroup$ – Ross Millikan Mar 13 '16 at 2:33

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