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Liquids and Solids

Liquids and Solids. Chapter 12. 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. Fluid. Substance that can flow and therefore take the shape of its container.

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Liquids and Solids

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  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

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