1. Phases in Detail Gases

2. Molecules spread out and fill spaces they are given due to their weak intermolecular forces of attraction There are large spaces between gas particles (molecules)

3. Gases Evaporation

4. Takes place at all temperatures on the liquid/vapor boundary

5. Evaporation Continued Vapor- a gaseous phase of a substance that is a liquid or solid at normal conditions Once liquid particles have absorbed enough energy to overcome attractive forces, they become vapor Vapor pressure- gas particles exert pressure on the liquid when they evaporate 1. In a closed system, the pressure increases Evaporation increases with an increase in temperature

6. Gases Continued Reference Table H

7. Vapor pressure increases as temperature increases 101.3 k P a – standard pressure (table A) 1 atm, 760 torr, 760 mmHg are also values for standard pressure Normal boiling point – when the vapor pressure is equal to atmospheric pressure When a substance boils, evaporation occurs throughout the liquid

8. Table H Continued Also measures the strength of intermolecular forces (forces between molecules) 1. If VP is high, attraction between molecules is weak (propanone) 2. If vapor pressure is low, attraction between molecules is strong (ethanoic acid) Table H

9. Table H Continued At what temperature will water boil if the pressure is 50 k P a? What is the normal boiling point of ethanol?