Ionic Solids

1. The extremes in dipole-dipole forces-atoms are actually held together by opposite charges. • Huge melting and boiling points. • Atoms are locked in lattice so hard and brittle. • Every electron is accounted for so they are poor conductors-good insulators. • Until melted or dissolved. Ionic Solids

2. Phase Changes

3. Vaporization - change from liquid to gas at boiling point. • Evaporation - change from liquid to gas below boiling point • Heat (or Enthalpy) of Vaporization (DHvap )- the energy required to vaporize 1 mol at 1 atm. Vapor Pressure

4. Vaporization is an endothermic process - it requires heat. • Energy is required to overcome intermolecular forces. • Responsible for cool beaches. • Why we sweat.

5. Change from gas to liquid. • Achieves a dynamic equilibrium with vaporization in a closed system. • What is a closed system? • A closed system means matter can’t go in or out. • Put a cork in it. • What the heck is a “dynamic equilibrium?” Condensation

6. When first sealed the molecules gradually escape the surface of the liquid Dynamic equilibrium

7. When first sealed the molecules gradually escape the surface of the liquid • As the molecules build up above the liquid some condense back to a liquid. Dynamic equilibrium

8. As time goes by the rate of vaporization remains constant • but the rate of condensation increases because there are more molecules to condense. • Equilibrium is reached when… Dynamic equilibrium

9. Rate of Vaporization = Rate of Condensation • Molecules are constantly changing phase “Dynamic” • The total amount of liquid and vapor remains constant “Equilibrium” Dynamic equilibrium

10. The pressure above the liquid at equilibrium. • Liquids with high vapor pressures evaporate easily. • They are called volatile. • Decreases with increasing intermolecular forces. • Bigger molecules (bigger LDF) • More polar molecules (dipole-dipole) • Increases with increasing temperature. • Easily measured in a barometer. Vapor pressure

11. Vacuum Patm= 760 torr Dish of Hg A barometer will hold a column of mercury 760 mm high at one atm

12. Vacuum Patm= 760 torr Dish of Hg A barometer will hold a column of mercury 760 mm high at one atm. If we inject a volatile liquid in the barometer it will rise to the top of the mercury.

13. Water A barometer will hold a column of mercury 760 mm high at one atm. If we inject a volatile liquid in the barometer it will rise to the top of the mercury. There it will vaporize and push the column of mercury down. Patm= 760 torr Dish of Hg

14. The mercury is pushed down by the vapor pressure. • Patm = PHg + Pvap • Patm - PHg = Pvap • 760 - 736 = 24 torr Water Vapor 736 mm Hg Dish of Hg

15. Energy needed to overcome intermolecular forces T1 # of molecules Temperature Effect Kinetic energy

16. At higher temperature more molecules have enough energy - higher vapor pressure. Energy needed to overcome intermolecular forces Energy needed to overcome intermolecular forces T1 T1 # of molecules T2 Kinetic energy

17. Clausius-Clapeyronequation can be used to determine the VP of a liquid at a different temperature or find the heat of vaporization. In an experiment plotting 1/T will result in a line whose slope is equal to -∆H/R where R = 8.3145 J mol-1K-1 DHvap is the heat of vaporization in J/mol Using Vapor Pressure Data

18. The vapor pressure of water at 25°C is 23.8 torr, and the heat of vaporization of water at 25°C is 43.9 kJ/mol. Calculate the vapor pressure at 50. °C • Ans: 93.7 torr • Determine the boiling point of water in Breckenridge, CO where the atmospheric pressure is 520 torr. For water, ∆Hvap = 40.7 kJ/mol. At 100. °C the VP of water is 1.00 atm. • Ans: 362 K Examples

19. The graph of temperature versus heat applied is called a heating curve. • The temperature a solid turns to a liquid is the melting point. • The energy required to accomplish this change is called the Heat (or Enthalpy) of Fusion DHfus Changes of state

20. Water phase changes constant Temperature remains __________ during a phase change. Energy

21. Melting point is determined by the vapor pressure of the solid and the liquid. • At the melting point the vapor pressure of the solid = vapor pressure of the liquid Melting Point

22. Water Vapor Vapor Solid Water Liquid Water

23. Water Vapor Vapor Solid Water Liquid Water If the vapor pressure of the solid is higher than that of the liquid the solid will release molecules to achieve equilibrium.

24. Water Vapor Vapor Solid Water Liquid Water • While the molecules of condense to a liquid.

25. Water Vapor Vapor Solid Water Liquid Water • This can only happen if the temperature is above the freezing point since solid is turning to liquid.

26. Water Vapor Vapor Solid Water Liquid Water • If the vapor pressure of the liquid is higher than that of the solid, the liquid will release molecules to achieve equilibrium.

27. Water Vapor Vapor Solid Water Liquid Water • While the molecules condense to a solid.

28. Water Vapor Vapor Solid Water Liquid Water • The temperature must be below the freezing point since the liquid is turning to a solid.

29. Water Vapor Vapor Solid Water Liquid Water • If the vapor pressure of the solid and liquid are equal, the solid and liquid are vaporizing and condensing at the same rate. The Melting point.

30. Reached when the vapor pressure equals the external pressure. • Normal boiling point is the boiling point at 1 atm pressure. • Superheating - Heating above the boiling point. • Heating too quickly results in “bumping” and can ruin an experiment. Boiling chips prevent this from happening. • Supercooling - Cooling below the freezing point. Boiling Point

31. Represents phases as a function of temperature and pressure. • Critical temperature: temperature above which the vapor can not be liquefied. • Critical pressure: pressure required to liquefy AT the critical temperature. • Critical point: critical temperature and pressure (for water, Tc = 374°C and 218 atm). • Triple point: Point at which all three states can exist. Phase Diagram

32. Phase changes by Name

33. Water

34. Carbon dioxide

35. Carbon

36. Sulfur