Liquids and Solids

1. Liquids and Solids Chapter 12

2. Liquid • Has a definite volume and indefinite shape • Particles are in constant motion • Closer together than gases • Less kinetic energy than gases • Greater attractive forces than gases Chemistry chapter 12

3. Fluid • Substance that can flow and therefore take the shape of its container Chemistry chapter 12

4. Fluid density • At normal pressure, most liquids are thousands of times denser than their gases. • Particles are closer together • Different liquids can vary greatly in density Chemistry chapter 12

5. Density Chemistry chapter 12

6. Incompressibility • Liquids are much less compressible than gases • Particles are closer together • Liquids can transmit pressure throughout themselves Chemistry chapter 12

7. Diffusion • Liquids diffuse in other liquids in which they can dissolve • Much slower than gases • Particles closer together • Attraction between particles slows them down • Faster at higher temperatures • More kinetic energy Chemistry chapter 12

8. Surface Tension • Force that pulls parts of a liquid’s surface together, causing it to have the smallest possible size • From attractive forces between molecules • Liquid droplets take a spherical shape Chemistry chapter 12

9. Capillary action • The attraction of the surface of a liquid to the surface of a solid • Causes meniscus • Water can travel up paper • Water traveling up a plant • Drawing blood in capillary tube Chemistry chapter 12

10. Vaporization • Changing from a liquid to a gas • Evaporation • Higher energy particles escape from the surface of a nonboiling liquid • perfume • Boiling • Bubbles of vapor that appear throughout the liquid and travel to the surface Chemistry chapter 12

11. Freezing • Changing a liquid to a solid by removing heat • Energy of particles decreases until they are pulled into a more orderly arrangement Chemistry chapter 12

12. Discussion • Describe the liquid state using kinetic molecular theory. • Explain why liquids in a test tube form a meniscus. • Compare and contrast vaporization and evaporation. Chemistry chapter 12

13. Solid • Has definite volume and definite shape • Particles are in constant motion • Much closer together than liquid or gas • Much stronger intermolecular forces • Held in relatively fixed position – only vibrate • Most ordered state of matter Chemistry chapter 12

14. High density and incompressibility • Substances are generally the most dense in the solid state • Slightly denser than liquids, much denser than gases • Virtually incompressible • Sometimes we compress air pockets in the solids • Wood, cork, etc. Chemistry chapter 12

15. Diffusion • Very, very slow • A few atoms may diffuse if clamped together for a long time Chemistry chapter 12

16. Melting • Change of a solid to a liquid by addition of heat • Melting point – temperature at which something melts Chemistry chapter 12

17. Crystalline solids • Consist of crystals • Particles are arranged in an orderly, geometric, repeating pattern • Fragments have geometric shapes • Have definite melting points • When the crystal structure breaks apart Chemistry chapter 12

18. Crystal structure • Total three-dimensional arrangement of particles in a crystal Chemistry chapter 12

19. Lattice • Coordinate system that represents the arrangement of particles in a crystal. Chemistry chapter 12

20. Unit cell • Smallest portion of a crystal lattice that shows the 3D pattern of the entire lattice • Each crystal lattice contains many unit cells packed together • Has one of seven types of symmetry – see page 369 Chemistry chapter 12

21. Ionic crystals • Positive and negative ions in a regular pattern • Hard and brittle • High melting points • Good insulators Chemistry chapter 12

22. Covalent network crystals • Individual atoms connected by covalent bonds • Giant molecules • Diamond • Quartz • Very hard and brittle • Rather high melting points • Nonconductors or semiconductors Chemistry chapter 12

23. Metallic crystals • Metal atoms surrounded by a sea of electrons • High electrical conductivity • Varying melting points Chemistry chapter 12

24. Covalent molecular crystals • Covalently bonded molecules held together by intermolecular forces • Low melting points • Easily vaporized • Relatively soft • Good insulators Chemistry chapter 12

25. Amorphous solids • Noncrystalline solids • The particles are arranged randomly • Glass • Plastics • Can be molded • Fragments have irregular shapes Chemistry chapter 12

26. Amorphous solids • Made by cooling molten substances in a way that prevents crystallization • Also called supercooled fluids • Retain certain fluid characteristics even at temperatures at which they appear to be solid • Can flow over a wide range of temperatures Chemistry chapter 12

27. Discuss • Account for each of the following properties of solids: • Definite volume • Relatively high density • Extremely low rate of diffusion • What is the difference between an amorphous solid and a crystalline solid? Chemistry chapter 12

28. Possible changes of state • Melting: solid to liquid • Sublimation: solid to gas • Freezing: liquid to solid • Vaporization: liquid to gas • Condensation: gas to liquid • Deposition: gas to solid Chemistry chapter 12

29. Closed system • Matter cannot enter or leave, but energy can Chemistry chapter 12

30. Equilibrium • A dynamic condition in which two opposing changes occur at equal rates in a closed system. • The same number of particles are entering and leaving. • The total number stays the same. Chemistry chapter 12

31. Equilibrium Chemistry chapter 12

32. Phase • Any part of a system that has uniform composition and properties. • Liquid or gas Chemistry chapter 12

33. An Equilibrium equation • When a substance changes state, it either absorbs or gives off energy, usually as heat. Chemistry chapter 12

34. Le Châtelier’s Principle • A system remains in equilibrium until a stress occurs on the system. • Stress: change in concentration, pressure, or temperature • When a system is disturbed by a stress, it attains a new equilibrium position that minimizes the stress. Chemistry chapter 12

35. Shifting equilibrium • Shifts to the right or left, depending on which part of the equation gains concentration. • See table 12-3 on page 375 Chemistry chapter 12

36. Equilibrium vapor pressure • The pressure exerted by a vapor in equilibrium with its liquid at a given temperature • Increases as temperature increases • But not directly Chemistry chapter 12

37. Kinetic-molecular theory • Increasing the temperature increases the energy and speed of the liquid particles • This means more particles evaporate, leading to higher vapor pressure Chemistry chapter 12

38. Caution • Equilibrium vapor pressure depends only on temperature. • If the system is not in equilibrium, gas laws must be used. Chemistry chapter 12

39. Volatile liquids • Evaporate easily • Weak forces of attraction between particles • Ether, acetone Chemistry chapter 12

40. Boiling • Conversion of a liquid to a vapor within the liquid as well as at the surface. • Occurs when the equilibrium vapor pressure equals atmospheric pressure. • All the heat absorbed goes to evaporate the liquid, so the temperature remains constant. Chemistry chapter 12

41. Chemistry chapter 12

42. Cooking • If atmospheric pressure is lower (high altitudes), liquids boil at lower temperatures and food takes longer to cook. • If the pressure is increased (pressure cooker), liquids boil at higher temperatures and food cooks faster. • If the pressure is decreased, it boils at low enough temperatures to avoid scorching milk and sugar. (evaporated and sweetened condensed milk) Chemistry chapter 12

43. Molar heat of vaporization • The amount of energy needed to vaporize one mole of liquid at its boiling point. • (or the amount of energy released when one mole of vapor condenses) • A measure of the attraction between particles. Chemistry chapter 12

44. Normal freezing point • Temperature at which the solid and liquid are in equilibrium at 1 atm pressure. • When a liquid freezes, energy is lost and order is gained. Chemistry chapter 12

45. Clarification • Boiling point is the same as condensation point. • Freezing point is the same as melting point. Chemistry chapter 12

46. Molar heat of fusion • The amount of heat energy required to melt one mole of solid at its melting point • (or the amount of energy released when one mole of a liquid freezes) • Depends on the attraction between particles. Chemistry chapter 12

47. Phase diagram • A graph of pressure versus temperature that shows the conditions under which the phases of a substance exist • Reveals how the states of a system change with changes in temperature or pressure Chemistry chapter 12

48. Water’s phase diagram Chemistry chapter 12

49. Curves on diagram • AB shows where solid and vapor can exist at equilibrium • AC shows liquid and vapor at equilibrium • AD shows solid and liquid at equilibrium • Usually a positive slope, but water is different Chemistry chapter 12

50. Triple point • Point A • Shows the temperature and pressure at which solid, liquid, and vapor can exist in equilibrium Chemistry chapter 12