1. Chapter 7 Phase Changes

2. Some things to think about

4. Two allotropes of Carbon

5. Dynamic Equilibrium A dynamic equilibrium can be established between either a (liquid and its vapor) or a (saturated solution and its solute). –L/Vthe # of particles leaving the liquid to become a vapor equals the # of particles returning to the liquid –SS/Sthe # of solid particles dissolving equals the # if dissolved particles reattaching to the solid

6. Boiling Point When the vapor pressure of a liquid reaches atmospheric pressure, the substance will boil. Normal boiling occurs at normal atmospheric pressure. –Remember normal atmospheric pressure can be 1 atm, 760 mmHg, or 101.3 kPa

7. Boiling Point Curves A boiling point curve represents all the temperatures at which a liquid will boil at various pressures. –If you raise the pressure, the liquid will boil at a higher temperature. –If you lower the pressure, the liquid will boil at a lower temperature.

8. Volatile vs nonvolatile VolatileNonvolatile Normal BPRelatively lowRelatively high Vapor pressureRelatively highRelatively low Does it evaporate easily? YesNo Intermolecular forces WeakStrong

9. Let’s look at a boiling pt curve

10. Heating curve

11. Heat of fusion Heat of fusion is the amount of energy needed to melt one gram of a substance. –Units are usually J/g The molar heat of fusion is the amount of energy needed to melt one mole of a substance. –Units are usually kJ/mol Heat of fusion is also used for freezing (although this is the energy given off)

12. Heat of vaporization Heat of vaporization is the amount of energy needed to boil one gram of a substance. –Units are usually J/g The molar heat of vaporization is the amount of energy needed to boil one mole of a substance. –Units are usually kJ/mol Heat of vaporization is also used for condensing (although this is the energy given off)

13. Determining energy involved for heating curve Heat the solid Q = m solid c solid ∆t solid Melt the solidQ = m H f Heat the liquidQ = m liquid c liquid ∆t liquid Boil the liquidQ = m H v Heat the gasQ = m gas c gas ∆t gas #’s for water

14. Vapor Phase Diagrams Points of interest –Triple point –Critical point Critical temperature Critical pressure –Equilibrium lines –Normal bp and mp

15. Vapor Phase Diagram

16. Phase Changes Phase changeWhat changes∆heat MeltingSolid to liquidEndothermic FreezingLiquid to solidExothermic BoilingLiquid to gasEndothermic CondensingGas to liquidExothermic SublimingSolid to gasEndothermic DepositingGas to solidExothermic

17. Energy needed to melt ΔH fusion Energy needed to boil ΔH vaporization Energy needed to sublime ΔH sublimation ΔH sub = ΔH fus + ΔH vap

18. What to know for test? Volatile vs nonvolatile Affect of strength of intermolecular forces on vapor pressure Be able to read diagrams Be able to do math regarding heating curve Dynamic equilibrium