EK 1001 Physics #506:
EK 1001 Physics #507:
I believe these two questions are out of the EK 1001 Chem book, and not the physics book...
Water mainly undergoes vaporization in two ways-evaporation and boiling. Evaporation is possible for a range of temperatures when water is liquid, and is primarily a surface phenomenon, and will proceed (at a given temperature) until the rate at which molecules are escaping the liquid equals the rate at which they come crashing back down. This is usually defined as the characteristic vapor pressure of the substance. If the liquid is open to the air (the atmosphere), the vapor pressure just adds, as another partial pressure, to the overall atmospheric pressure pushing down on it.
Boiling is a related, but different, story. For the liquid to boil, the vapor cannot just remain a tiny fraction of the local pressure above the liquid, and thermal energy must be added to it to increase the partial pressure of the vapor until it equals the atmospheric pressure pushing down. At this point the surface-type evaporation becomes a bulk vaporization, and the entire mass is free to eventually convert into the gas phase, which is why you can see bubbles forming and floating up to the top from within a pot of boiling water, and not just from the surface as in evaporation. This is why the the vapor pressure MUST equal the total pressure, and is also why boiling water at higher altitudes (lower pressures) may require less time and energy input.
For the question on sublimation, the vapor pressure will be between the solid and it's corresponding vapor. This is nice because it already puts things in terms of sublimation, which happens to be a solid transitioning into a gas. You can't really copy-and-paste the concepts of boiling from liquid-gas equilibria in here, think of boiling more as a special case of evaporation, where molecules anywhere (not just on the surface) in the condensed phase are free to vaporize. Sublimation is simply saying that the solid is becoming a gas; therefore the rate at which the vapor is forming must be greater than the rate at which it is becoming solid again, regardless of how the actual partial pressure of the vapor compares to atmospheric pressure, as in boiling. Simple equilibrium problem here, in reality. I hope this helps.
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