The pressure exerted by a liquid’s vapor



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Liquids

SUBLIMATION: a change from the solid phase directly to the gas phase without passing through the liquid phase. Example =”dry ice”=solid carbon dioxide. This readily sublimes at room temp (think the “fog” along the floor of the stage in a concert) because it has WEAK IMF’s



  1. The pressure exerted by a liquid’s vapor

  2. As the temp of a liquid increases, its Avg KE increases so more molecules have the energy necessary to vaporize, therefore the liquid produces more vapor which results in a higher vapor pressure (more gas molecules means more gas pressure)

  3. Find temp on the X axis and smack into the curve for a particular liquid, then move your finger over to the Y axis and read he vapor pressure

  4. Reverse your steps to answer #3 above: Find the v.p. on the Y axis, smack into your liquid’s curve, then move your finger down and read the temp on the x axis.

  5. Easily vaporized

  6. Pick any temp off the x axis that will intersect all the curves. The liquid with the highest vapor pressure is the most volatile because it has put the most vapor atop its own surface BECAUSE IT HAS THE WEAKEST IMF’s

  7. The liquid with the strongest IMF’s is most “resistant” to vaporizing therefore it should have the lowest v.p. of any liquid at any given temp.

  8. See answer #6

  9. Both are a phase change from liquid to gas but evap only takes place at the surface of a liquid and boiling takes place throughout a liquid AND can only occur when the liquid’s v.p. = atmospheric pressure

  10. If you have to match atmospheric pressure to boil and atmospheric pressure changes with altitude, a liquid’s boiling point will change with changes in altitude

  11. Because boiling point changes, a “norm” had to be chosen. Normal boiling point becomes the temp you must raise your liquid to such that its v.p. = STANDARD ATMOSPHERIC pressure

  12. Find a dotted line indicating standard pressure either in KPa, torr, or atmospheres, smack that line into the liquid’s curve and read down to the temp on the x axis

  13. Heat of vaporization is the heat necessary to vaporize a liquid. The liquid with the strongest IMF’s will require the most heat to become vaporized

  14. The liquid with the lowest heat of vaporization is the liquid with the weakest IMF’s.

  15. The water in the beaker under the bell jar began to form tiny bubbles as the vacuum pump removed more and more of the “atmosphere gases” above the liquid’s surface. The tiny bubbles forming THROUGHOUT the liquid quickly turned to a rolling boil. The water’s temp soon after was only about 20 celsius. This showed that water could boil at a temp OTHER THAN 100 celsius. This happens when the surrounding air pressure above the liquid is LOW.

  16. One cotton swab was dipped into acetone, another into ethanol, and a third into water. All swabs absorbed the same amount of liquid and all liquids were at the same temp. A streak of each was drawn across the black labtop at the same time. The acetone evaporated the fastest, then the ethanol and then the water, which took substantially longer than the other 2 liquids. This showed that acetone had the weakest IMF’s and water the strongest.

  17. Evaporation is actually a cooling process: recall that temp is a measure of AVERAGE KE, therefore all the water molecules in a sample (as say on a wet towel) are not at the same temp. The ones at the higher temp evaporate first

leaving behind the ones at a lower temp and so make the towel or say your wet arm feel colder). Rubbing alcohol was rubbed on children who had high fevers as a way to quickly reduce their surface temps because alcohol has weak IMF’s in general and so evaporates quickly as say compared to waiting for water to evaporate.


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