2. NOTES: 13.2-13.4 Relationship Between Gases & Liquids; Phase Changes & Phase Diagrams

3. The Nature of Liquids ● like the particles in a gas, the particles in a liquid also have kinetic energy ● like gases, liquids have an indefinite shape (they conform to the shape of their containers) ● however, there is a key difference between gases and liquids…

4. The Nature of Liquids ● the particles in a liquid are attracted to one another…this keeps the particles close together! ● as a result, liquids have a DEFINITE VOLUME (unlike gases!) ● liquids are MUCH more dense than gases…increasing the pressure on a liquid has hardly any effect on its volume (same is true for solids)

6. Changes of State:

8. VAPORIZATION: ● VAPORIZATION: the conversion of a liquid to a gas, or vapor

9. EVAPORATION: ● EVAPORATION: the conversion of a liquid to a gas at the surface of a liquid that is NOT boiling ● most molecules in a liquid don’t have enough KE to overcome the attractive forces of the liquid & escape into the gas state

10. EVAPORATION: ● a liquid evaporates faster when heated…WHY? ● heating a liquid increases the average KE of its particles…more particles are able to escape to the gas state!

14. EVAPORATION: ● the particles with the highest KE escape first…as a result… ● the particles left in the liquid have a lower average KE than the particles that escaped…so, evaporation is a COOLING PROCESS (the liquid left behind is cooler)

15. EVAPORATION: ● this process is called EVAPORATIVE COOLING ● important for living organisms & ecosystems in maintaining temperatures…including YOU!

16. Evaporative Cooling!

17. CONDENSATION: ● CONDENSATION: the change of state from gas to liquid (the opposite of vaporization)

18. BOILING: ● In order to understand boiling, you must first understand something called vapor pressure.

19. VAPOR PRESSURE: ● Every liquid has a property associated with it called vapor pressure. ● It depends significantly upon temperature…vapor pressure increases with increasing temperature.

20. ● Consider a liquid in a closed container. ● At first the liquid level goes down, then it stays constant.

21. Time Rate Rate of Evaporation Rate of Condensation ● The pressure in the container at the equilibrium point (between liquid & vapor) is the vapor pressure. Rates are equal. (Equilibrium Point)

22. BOILING: ● BOILING = a rapid state of evaporation that takes place within the liquid as well as at it’s surface. ● Boiling takes place when the vapor pressure of the liquid equals the external (surrounding, or applied) pressure.

23. BOILING POINT: ● BOILING POINT = the temperature at which the vapor pressure of a liquid is just equal to the external (applied) pressure on the liquid…the temperature at which a liquid boils!

25. Heat Entering Water Heat Leaving Water Boiling is a Cooling Effect! Liquid stays at a constant temp. (100°C)

26. Vapor Pressure of Water: 110 o C 100 o C 75 o C 20 o C 0oC0oC 1074 mm Hg 760 300 17 4.6

27. Vapor Pressure of Water 110 o C 100 o C 75 o C 20 o C 0oC0oC 1074 mm Hg 760 300 17 4.6 Room Pressure Room Temp

28. 110 o C 100 o C 75 o C 20 o C 0oC0oC 1074 Torr 760 300 17 4.6 Room Pressure Room Temp Normal Boiling:

29. 110 o C 100 o C 75 o C 20 o C 0oC0oC 1074 Torr 760 300 17 4.6 Room Pressure Room Temp Boiling at Room Temperature

30. Pressure Cookers

31. 110 o C 100 o C 75 o C 20 o C 0oC0oC 1074 Torr 760 300 17 4.6 Pressure Cookers Cook Faster Because The Boiling Water is Hotter

33. MELTING: ● MELTING: the change of state from solid to liquid; energy (heat) is absorbed by the substance that is melting. ● Melting Point = temp. at which a solid changes into liquid

34. FREEZING: ● FREEZING: the change of state from liquid to solid. ● Freezing Point = temp. at which a liquid changes into solid

36. Boiling Point Melting Point Gas Liquid Solid

37. SUBLIMATION: ● SUBLIMATION: the change of a substance from a solid to a gas (vapor) without passing through the liquid state

38. PHASE DIAGRAMS: ● a PHASE DIAGRAM gives the conditions of temperature & pressure at which a substance exists as solid, liquid, or gas (vapor). ● the conditions of pressure & temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the 2 regions representing the phases

39. Phase Diagram for Water:

40. Phase Diagram Features: ● BOUNDARY LINE: where 2 phases are in equilibrium ● TRIPLE POINT: temp / pressure at which all 3 phases are in equilibrium ● CRITICAL POINT: temp / pressure above which a gas can no longer be condensed to liquid **above the critical point, a substance is known as a supercritical fluid

41. Phase Diagram for CO 2 :