Yttrium2
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pressure above substance in jar
When a substance that sublimes or evaporates is placed into a container, it will evap/sublime until there is a certain pressure in the jar, that
prevents more from turning to gas? Is this property vapor pressure? If not what is it?
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Zombie
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If you are talking about a sealed container then yes. Vapor pressure is built.
The point where no more can evaporate is called Equilibrium.
They tried to have me "put to sleep" so I came back to return the favor.
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Crowfjord
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When the vapor pressure of a substance reaches or exceeds the pressure of its system/surroundings, then it boils. I'm not sure about sublimation,
though. I think that may be a little different.
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annaandherdad
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No, equilibrium is reached when the vapor pressure of the substance (either solid or liquid) is equal to the *partial pressure* of that same substance
in the vapor phase. The partial pressure of other substances in the gas phase doesn't matter.
There are assumptions and approximations in this statement, which is nevertheless valid under many practical circumstances. For example, it assumes
there is no chemical reaction between the substance that is evaporating and the rest of the gas (e.g., iodine and air). It also assumes an ideal gas
for the vapor phase, thus there are corrections when the pressure is high.
Correction: Yes, you are right, a liquid boils when its vapor pressure equals the total pressure of the surroundings. However, what I stated about
the conditions for equilibrium are correct (equilibrium at any temperature).
[Edited on 19-3-2015 by annaandherdad]
Any other SF Bay chemists?
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Loptr
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Quote: Originally posted by annaandherdad  | No, equilibrium is reached when the vapor pressure of the substance (either solid or liquid) is equal to the *partial pressure* of that same substance
in the vapor phase. The partial pressure of other substances in the gas phase doesn't matter.
There are assumptions and approximations in this statement, which is nevertheless valid under many practical circumstances. For example, it assumes
there is no chemical reaction between the substance that is evaporating and the rest of the gas (e.g., iodine and air). It also assumes an ideal gas
for the vapor phase, thus there are corrections when the pressure is high.
Correction: Yes, you are right, a liquid boils when its vapor pressure equals the total pressure of the surroundings. However, what I stated about
the conditions for equilibrium are correct (equilibrium at any temperature).
[Edited on 19-3-2015 by annaandherdad] |
It should also be defined that the partial pressure is the vapor pressure of a single component within a mixture that contributed to the vapor
pressure of the system. And as annaandherdad said, it doesn't account for other components that might also be in the gas phase.
A phase transition occurs as the vapor pressure of a substance approaches or moves farther away from the equilibrium of the vapor pressure and the
partial vapor pressure in the gas phase. Once the equilibrium is met, the phase transition effectively stops, or rather you see equal exchange between
phases, which keeps the proportions in check and a halt in loss of the liquid phase due to evaporation.
[Edited on 19-3-2015 by Loptr]
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