I am studying the enthalpy of fusion, enthalpy of vaporization, and latent heat. I’m not extremely skilled in physics or formulas so would appreciate answers in simple form. To take the question a bit farther if I were to drop a one ounce piece of ice into the vacuum of space as well as dump a one ounce glass of water near the same area would the water vaporize and the ice stay frozen such as a comet? If not what factors determine the changing of state of the ice? I would assume any ice that had enough heat/radiation to melt it would skip the water state pretty much and boil away to vapor due to the vacuum. Is this correct?
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2$\begingroup$ Well, it doesn't instantly boil, and the latent heat input causes the water to cool down. Make it cold enough and there isn't heat around to release any. Thermodynamics vs kinetics at work. $\endgroup$– Jon CusterCommented Jul 21, 2022 at 20:37
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$\begingroup$ Okay I retract the word instantly for “quickly”.. but that doesn’t really answer my questions. So are you saying that if it was extremely cold close to absolute zero.. the ice would stay frozen while the water would vaporize due to latent heat? Isn’t that kind of contradictory.. one staying frozen while the other vaporizers? $\endgroup$– Scott SlowikCommented Jul 21, 2022 at 20:55
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2$\begingroup$ If there is not much energy in the system (i.e. it is really cold), then where does an atom/molecule get the energy needed to depart? $\endgroup$– Jon CusterCommented Jul 21, 2022 at 20:58
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3$\begingroup$ The other thing to remember is that vapor pressures (above either a liquid or a solid) are a function of the temperature of the object (an exponential function of the temperature). The colder the object, the lower the equilibrium vapor pressure. For very cold objects, the atoms lost to the solid are not moving fast at all, and essentially become an atmosphere around the object. $\endgroup$– Jon CusterCommented Jul 21, 2022 at 21:04
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2$\begingroup$ A useful calculation would be the vapor pressure of ice versus temperature, and from that an estimation of the rate of sublimation per unit area as a function of temperature in vacuum. Note that comets contain non-ice solids ("dirt"), so as the cold ice sublimates the dirt will tend to migrate to the surface. The situation changes if the comet is qarmed by sunlight, so that the sublimation becomes rapid enough to eject dust from the surface with the water vapor. $\endgroup$– rob ♦Commented Jul 21, 2022 at 21:18
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Here's my simple explanation.
Assume a mass of water at say 40 degrees F is thrown into space. Space has a low pressure and a low temperature. Water is lost of due to vaporization, but the water is also cooled by the energy required to cause vaporization and radiative heat transfer to outer space. If the quantity of water is large enough, it will cool to the temperature of outer space (-455 F) and become ice before it has all vaporized, even at the extremely low pressure of outer space.
answered Jul 21, 2022 at 21:23
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$\begingroup$ Thank you. Simple and easy for me to understand. So as I see it then if in a large enough quantity the water will vaporize to some degree while using up the energy (BTUs) from the rest of the water.. but at some point there will be a point of equalization where there isn’t enough latent heat to provide for the change of state (vaporization) and and that point the remaining water will freeze since it can’t do anything else. I think I understand now. $\endgroup$ Commented Jul 22, 2022 at 1:02