Solid-Vapour Coexistence

  • Thread starter Red_CCF
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In summary, the conversation discusses the possibility of ice and water vapor coexisting at certain temperatures and pressures due to the presence of air, similar to how liquid water and water vapor coexist in psychrometrics. The concept of sublimation and its relation to ice in the presence of air is also mentioned. The conversation ends with a discussion on the different types of phase transitions and their similarities.
  • #1
Red_CCF
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Hi

I was wondering if, for water, is it possible for ice and water vapour to co-exist at some temperature and pressure due to the presence of air (not phase equilibrium among itself) like we see for liquid water and water vapour in psychrometrics, why or why not?

Thanks.
 
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  • #2
Red_CCF said:
Hi

I was wondering if, for water, is it possible for ice and water vapour to co-exist at some temperature and pressure due to the presence of air (not phase equilibrium among itself) like we see for liquid water and water vapour in psychrometrics, why or why not?

Thanks.

Any solid coexists with a gas phase, because all materials have some non-zero vapor pressure. What do you mean by "due to the presence of air"?
 
  • #3
Mapes said:
Any solid coexists with a gas phase, because all materials have some non-zero vapor pressure. What do you mean by "due to the presence of air"?

Hi

Sorry for not being clear, my question is kind of confusing. For water, liquid and vapour can coexist (at say 1 atm and 25 degrees celcius) when exposed to air which explains how a cup of water becomes empty over time at conditions below its phase change on the phase diagram. I was wondering if such phenomenon is also possible if we have ice instead of liquid water (is there a condition where if I put a piece of ice in a glass exposed to air it would turn into vapour directly without melting). I hope this is less confusing.

Thanks
 
  • #4
Red_CCF said:
Hi

Sorry for not being clear, my question is kind of confusing. For water, liquid and vapour can coexist (at say 1 atm and 25 degrees celcius) when exposed to air which explains how a cup of water becomes empty over time at conditions below its phase change on the phase diagram. I was wondering if such phenomenon is also possible if we have ice instead of liquid water (is there a condition where if I put a piece of ice in a glass exposed to air it would turn into vapour directly without melting). I hope this is less confusing.

Thanks

It is possible and it is called http://en.wikipedia.org/wiki/Sublimation_%28phase_transition%29" [Broken].
 
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  • #5
Mapes said:
It is possible and it is called http://en.wikipedia.org/wiki/Sublimation_%28phase_transition%29" [Broken].

Hi

Thanks for the response. Sublimation still occurs when the system contains a pure substance (e.g. water) and is based on the phase diagram. For a cup of liquid water that is left at room temperature and pressure, it becomes vapour because of the presence of air and the psychrometric chart is used to determine humidity/how much vapour etc. as the phase diagram is only valid for a closed system with pure substance. I was wondering if such chart/phenomenon exists if the water was ice to begin with and whether ice can directly vaporize if the system contains air and the ice not just H2O alone.
 
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  • #6
Red_CCF said:
Sublimation still occurs when the system contains a pure substance (e.g. water)

No; sublimation is a phase change from the solid to the gas state. Evaporation is a phase change from the liquid state (e.g., water) to the gas state.

Red_CCF said:
I was wondering if such chart/phenomenon exists if the water was ice to begin with and whether ice can directly vaporize if the system contains air and the ice not just H2O alone.

Yes, ice still sublimates even if it is surrounded by air. Some of the H2O molecules bounce off air molecules and condense back on the ice, but the net reaction is from ice to gas. Try leaving an ice tray in your freezer for a few months; the ice cubes will gradually disappear. (Even if the ice is mixed with another substance such as salt. Note that the salt's vapor pressure is far too low for it to evaporate noticeably within a time span of years. The salt would be left behind.)
 
  • #7
Mapes said:
No; sublimation is a phase change from the solid to the gas state. Evaporation is a phase change from the liquid state (e.g., water) to the gas state.
Yes, ice still sublimates even if it is surrounded by air. Some of the H2 molecules bounce off air molecules and condense back on the ice, but the net reaction is from ice to gas. Try leaving an ice tray in your freezer for a few months; the ice cubes will gradually disappear.

Hi

Thanks for clearing that up!

Is there a chart similar to the psychrometrics chart that describes this ice to vapour transition in the presence of air under difference conditions?

Also, how come we have boiling and evaporation for liquid to vapour transition? Do we have two types of transitions for solid to liquid or solid to ice?

Thanks
 
  • #8
Red_CCF said:
Is there a chart similar to the psychrometrics chart that describes this ice to vapour transition in the presence of air under difference conditions?

Perhaps you can make one!

Red_CCF said:
Also, how come we have boiling and evaporation for liquid to vapour transition?

Boiling is a special case of evaporation in which the vapor pressure has exceeded the atmospheric pressure.
 
  • #9
Mapes said:
Perhaps you can make one!



Boiling is a special case of evaporation in which the vapor pressure has exceeded the atmospheric pressure.

Is melting more synonymous to boiling or more to evaporation? What about sublimation?
 
  • #10
Red_CCF said:
Is melting more synonymous to boiling or more to evaporation? What about sublimation?

What do you think? Melting is defined as a change of state from what to what?
 
  • #12
Mapes said:
What do you think? Melting is defined as a change of state from what to what?

From solid to liquid? So I guess closer to evaporation?
 
  • #13
Red_CCF said:
From solid to liquid? So I guess closer to evaporation?

I'm not sure why a solid-to-liquid transition would be more like a liquid-to-gas transition and less like a solid-to-gas transition... They all seem pretty distinct.
 
  • #14
Mapes said:
I'm not sure why a solid-to-liquid transition would be more like a liquid-to-gas transition and less like a solid-to-gas transition... They all seem pretty distinct.

I can see how this question is kind of weird. I was thinking that, in boiling there is bubble/phase change in the bulk of the liquid, so I'm just wondering if in melting does it occur from the outside inwards or within the bulk of the solid.
 
  • #15
Red_CCF said:
I can see how this question is kind of weird. I was thinking that, in boiling there is bubble/phase change in the bulk of the liquid, so I'm just wondering if in melting does it occur from the outside inwards or within the bulk of the solid.

Boiling and melting will both generally occur preferentially closer to the heat source (assuming ample possible nucleation sites).
 
  • #16
Mapes said:
Boiling and melting will both generally occur preferentially closer to the heat source (assuming ample possible nucleation sites).

Hi

So am I correct to say that in boiling, the liquid closer to the heat source vaporizes first (i.e. from the outside inwards) and the bubble in the bulk of the liquid results from these vapors from the outside rising up?

Thanks very much
 
  • #17
Generally, yes.
 

1. What is solid-vapour coexistence?

Solid-vapour coexistence refers to the simultaneous presence of a solid phase and a vapour phase of the same substance in a closed system. This means that both the solid and vapour phases are in equilibrium with each other, and the amount of substance in each phase remains constant.

2. How does solid-vapour coexistence occur?

Solid-vapour coexistence occurs when a substance is heated to its boiling point, causing it to transition from a solid phase to a vapour phase. As the substance continues to be heated, the vapour pressure increases, and the amount of vapour in the system also increases. Eventually, a point of equilibrium is reached where the amount of solid and vapour remains constant.

3. Why is solid-vapour coexistence important in scientific research?

Solid-vapour coexistence is important in scientific research because it allows us to study the properties of a substance at specific temperatures and pressures. By controlling the conditions of solid-vapour coexistence, scientists can better understand the behaviour and characteristics of a substance, which can have practical applications in various fields such as materials science and chemistry.

4. How can solid-vapour coexistence be controlled?

Solid-vapour coexistence can be controlled by adjusting the temperature and pressure of the system. By changing these variables, the point of equilibrium between the solid and vapour phases can be manipulated, allowing for the study of different phases of a substance.

5. What are some real-world examples of solid-vapour coexistence?

One real-world example of solid-vapour coexistence is the process of sublimation, where a solid substance (such as dry ice) transitions directly into a vapour phase without going through a liquid phase. Another example is the coexistence of ice and water vapour in the Earth's atmosphere, which plays a significant role in the water cycle and weather patterns.

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