Changes of State

1. Changes of State 10.4

2. Definitions • Phase – any part of a system with uniform composition and properties. • Condensation – gas changes to a liquid • Molecules of liquid can evaporate and then condense and re-enter the liquid phase

3. Equilibrium • Condensation and evaporation can happen at the same rate… • Equilibrium – a dynamic condition in which 2 opposing changes occur at equal rates in a closed system • No net change in amt. of substance in either phase.

4. Equilibrium and Vapor Pressure • P is directly proportional to [ ] • Equilibrium vapor pressure – pressure exerted by vapor in equilibrium with its corresponding liquid at a given temp • Different for each liquid • The higher the bonding the _____the EVP • Think about the KMT

5. Definitions • Volatile Liquids – liquids that evaporate readily • __________ forces of attraction. • Boiling – conversion of a liquid to a vapor within the liquid as well as at the surface • Boiling point – the temp at which the equilibrium vapor pressure of the liquid = atm pressure

6. Boiling • The ________ the atm pressure, the lower the b.p. • Temp is constant while boiling • Normal atmospheric pressure = 1 atm, 760 torr, 101.325kPa • E needs to be + constantly to continue boiling

7. Molar Enthalpy of Vaporization • MEV – the amt of E as heat that is needed to vaporize 1 mol of liquid at the liquids b.p. at constant pressure. • ΔHv • Measure of attraction of particles

8. Freezing and Melting • Freezing – physical change of liquid to solid • Loss of E • Freezing point – the temp at which solid and liquid are at equilibrium at 1 atm • At f. p. particles have same amt of ave K. E.

9. Melting • At m.p. the solid and liquid have the same amt of k.e. also. • For pure crystalline solids, f.p. and m.p. are at the same temp.

10. Molar Enthalpy of fusion • Molar Enthalpy of fusion – the amount of energy as heat required to melt one mole of solid at the solids melting point.