1. By: Christine Bontempi Emily DeAngelis Vapor Pressure

2. Vapor Pressure • Vapor Pressure- the pressure exerted by a vapor in equilibrium with its liquid or solid phase

3. Explaining Vapor Pressure on the Molecular Level • When molecules in a liquid have enough kinetic energy to overcome the attractive forces, they change into the gas phase • Weaker attractive forces larger number of molecules evaporate & higher vapor pressure

4. Dynamic Equilibrium • As the number of gas-phase molecules increase, more gas-phase molecules condensate back into the liquid • Dynamic equilibrium- when evaporation and condensation occur at equal rates • In equilibrium, molecules continuously pass from the liquid state to the gas state and vice versa Vapor Pressure Video

5. Volatility and Vapor Pressure • Volatile liquids evaporate readily • Vapor spreads away from a liquid if vaporization occurs in an open container • Equilibrium is never reached and the liquid continues to evaporate to dryness • Substances with high vapor pressure (gasoline) evaporate more quickly than substances with a low vapor pressure (motor oil)

6. Temperature and Vapor Pressure • Vapor pressure increases with temperature • As the temperature increases, the molecules move more energetically and can escape easier Low Temperature High Temperature

7. Vapor Pressure is Directly Proportional to Temperature of a Liquid Water (line indicates boiling point)

8. Boiling Point and Vapor Pressure • Liquids boil when vapor pressure=external pressure • Temperature of boiling increases with increasing external pressure • Normal Boiling Point is the boiling point of a liquid at 1 atm pressure • The boiling point decreases as the altitude increases

9. Forces that affect Vapor Pressure • Surface Area: no affect • Type of Molecule: If the intermolecular forces between molecules are • Strong, vapor pressure is low • Weak, vapor pressure is high • Temperature: Higher temperature, more molecules evaporate

10. Review Questions PCl3 and AsCl3 are similar substances, with similar geometries and bonding modes. a. Which is more volatile at room temp? b. Which has a higher boiling point? c. Which has the larger intermolecular forces?

11. Review Questions Explain how each of the following affects the vapor pressure of a liquid: a. Volume of a liquid b. Temperature c. Intermolecular attractive forces

12. Works Cited http://www.chem.purdue.edu/gchelp/liquids/vpress.html http://urila.tripod.com/colligative.htm