SAMPLE - Experiment 3: Vapor Pressure of Water Purpose To...

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11 Experiment 3: Vapor Pressure of Water Purpose To measure the vapor pressure of water as a function of temperature, and to determine the value of ΔH vap for water. Equipment Needed 10 mL graduated cylinder, test tube tongs, tall form 1000 mL beaker, thermometer, hot plate or Bunsen burner Discussion Although the average kinetic energy of the molecules of a liquid is a function of temperature, the exact amount of energy of a specific molecu1e is random. At a given temperature, the energies of the molecules of a liquid are distributed about a mean value, with both very slow molecules and very fast molecules present. Even at low temperatures, there will be some molecules with a high amount of kinetic energy, and these fast molecules will be able to escape the attractive forces that tend to bind liquid molecules together. Because the number of fast molecules is a function of temperature, the rate at which liquid molecules escape into the vapor phase will be a function of temperature. Within the gas phase, molecules are moving randomly and are constantly entering into collisions with the each other and with the liquid phase. Interactions involving these slow moving gas molecules will usually result in one or more molecules loosing sufficient energy to cause it to condense back into a liquid. The rate at which this occurs depends strictly on the number of collisions which occur, which is directly proportional to the partial pressure of the vapor.
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This note was uploaded on 11/12/2011 for the course CHEM CHEM 2B taught by Professor Cabrera during the Spring '09 term at San Jose City College.

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SAMPLE - Experiment 3: Vapor Pressure of Water Purpose To...

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