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Chapter 5

  1. 1. GASES, LIQUIDS, AND SOLIDS CHAPTER 5 CHEM 103 • states of matter • gas laws • intermolecular forces • liquids • surface tension • vapor pressure • factors affecting boiling point • solids • phase changes
  2. 2. The states of matter
  3. 3. Which phase of matter has negligible interactions between molecules? 1. gas 2. liquid 3. solid 4. More than one answer is correct.
  4. 4. PRESSURE Pressure is defined as force per unit area and is expressed as: 1 atm = 760 mm Hg = 760 torr = 101,325 Pa MERCURY BAROMETER MANOMETER
  5. 5. Gas Laws PV = constant or P1V1 = P2V 2 BoyleBoyle’s law:’s law: for a fixed mass of gas at a constant temperature, the volume is inversely proportional to the pressure
  6. 6. Gaseous nitrogen in an air bag has a pressure of 745 mm Hg and a volume of 65.0 L. If the gas is transferred to a 25.0 L bag at the same temperature what is the new pressure? 1. 287 mm Hg 2. 48425 mm Hg 3. 1940 mm Hg 4. 1210625 mm Hg
  7. 7. CharlesCharles’s Law:’s Law: the volume of a fixed mass of gas at a constant pressure is directly proportional to the temperature in Kelvins (K). V T V1 T1 V2 T2 = a constant or =
  8. 8. P T P1 T1 P2 T2 = a constant or = Gay-LussacGay-Lussac’s Law’s Law:: for a fixed mass of gas at constant volume, the pressure is directly proportional to the temperature in kelvins (K).
  9. 9. Boyle’s law, Charles’s law and Gay- Lussac’s law can be combined into one law called the combined gas lawcombined gas law..
  10. 10. A gas occupies 3.00 L at 2.00 atm. Calculate its volume when the pressure is 10.15 atm at the same temperature. because the temperature is constant T1 = T2 P1 = 2.00 atm V1 = 3.00 LInitial: Final: P2 =10.15 atm V2 = ?
  11. 11. At a temperature of 273 K (0 °C) and a pressure of 1 atm (STP conditions), one mol of any gas occupies a volume of 22.4 L 22.4 L Avogadro’s Law Equal volumes of all gases at the same T and P contain the same number of moles.
  12. 12. Ideal Gas Law Avogadro’s law allows us to write a gas law that is valid not only for any P, V, and T but also for any mass of gas. Ideal gas law:Ideal gas law: PV = nRT P = pressure of the gas in atmospheres (atm) V = volume of the gas in liters (L) n = moles of the gas (mol) T = temperature in kelvins (K) R = ideal gas constantideal gas constant (a constant for all gases)
  13. 13. We find the value of RR by using the fact that 1.00 mol of any gas at STP occupies 22.4 L 1.00 mol of CH4 gas occupies 20.0 L at 1.00 atm. What is the temperature of the gas in kelvins? PVR = nT = (1.00 atm)(22.4 L) (1.00 mol)(273 K) = 0.0821 L•atm mol•K
  14. 14. How many moles of Nitrogen gas are in a 65 L cylinder with a pressure of 1.09 atm at 298 K? R= 0.082057 L atm/K mol 1. 2. 3. 4. 2.9
  15. 15. Gas Laws DaltonDalton’s law of partial pressures:’s law of partial pressures: the total pressure, PT, of a mixture of gases is the sum of the partial pressures of each individual gas: TTo a tank containing N2 at 2.0 atm and O2 at 1.0 atm we add an unknown quantity of CO2 until the total pressure in the tank is 4.6 atm. What is the partial pressure of CO2?
  16. 16. What is the partial pressure of argon, if the total pressure of the gas mixture is 5.8 atm and the partial pressures of the other gases are 2.7 atm? 1. 2.1 atm 2. 3.1 atm 3. 8.5 atm 4. 16 atm
  17. 17. Kinetic Molecular Theory Assumptions:  Gases consist of particles moving in random directions with various speeds.  Gas particles have no volume.  Gas particles have no attraction between them.  The average kinetic energy of gas particles is proportional to the temperature in kelvins.  Molecular collisions are elastic  Molecules collide with the walls of their container; these collisions constitute the pressure of the gas.
  18. 18. IDEAL vs REAL • Ideal gas:Ideal gas: follows the assumptions of the kinetic molecular theory. • Real gasesReal gases: atoms or molecules do occupy some volume and there are forces of attraction between their atoms or molecules. In reality there is no ideal gas, however at STP conditions most real gases behave close enough to ideal. Vm= real volume of 1 mol V°m= ideal volume of 1 mol
  19. 19. Which of the following is NOT true about real gases? 1. A gas particle will move faster as it is heated. 2. Gas particles have no volume. 3. Molecular collisions with walls of the container constitute the pressure of the gas. 4. There are forces of attraction between gas molecules.
  20. 20. Intermolecular Forces The strength of attractive forces between molecules determines whether any sample of matter is a gas, liquid, or solid. Near STP, the forces of attraction between molecules of most gases are so small that they can be ignored. When T decreases and/or P increases, the forces of attraction become important to the point that they cause condensation and ultimately solidification.  London forces  Dipole-dipole interactions  Hydrogen bonding
  21. 21. London Dispersion Forces London dispersion forces are the attraction between temporary induced dipoles.
  22. 22. London Dispersion Forces – Exist between all atoms and molecules. – They are the only forces of attraction between nonpolar molecules. – This force increases as the mass and number of electrons increases. – Even though these forces are very weak, they contribute significantly to the attractive forces between large molecules.
  23. 23. Dipole-Dipole Interactions Polar molecules contain permanent partial charges resulting in attractions between opposite partial charges between molecules. Dispersion forces are experienced in addition to dipole forces. Butane is a nonpolar molecule the only interactions between butane molecules are London forces. Acetone is a polar molecule; its molecules are held together in the liquid state by dipole-dipole interactions.
  24. 24. Hydrogen Bonds Force of attraction between the partial positive charge on a hydrogen bonded to an atom of high electronegativity, most commonly O, N, or F and the partial negative charge (unshared electrons) on a nearby O, N or F.
  25. 25. Table 6-2, p. 171 δ−
  26. 26. Which of the following is the strongest? 1. London Dispersion Forces 2. Dipole-Dipole Interactions 3. Hydrogen Bonds 4. Covalent Bonds
  27. 27. Liquids – As pressure increases in a real gas, its molecules come closer and closer with the result that attractions between molecules become important. – Forces of attraction among gas molecules condense it into a liquid. – In liquids, there is very little space between molecules; liquids are difficult to compress. – The density of liquids is much greater than that of gases because the same mass occupies a much smaller volume. – The position of molecules in a liquid is random and there is irregular space between them into which other molecules can slide; this causes liquids to be fluid.
  28. 28. Surface Tension The layer on the surface of a liquid produced by uneven intermolecular attractions at its surface. Surface tension is directly related to strength of the intermolecular attraction between molecules.
  29. 29. VAPOR PRESSURE When the equilibrium liquid  vapor is reached, the pressure produced by the vapor on the liquid remains constant as well as the number of vapor molecules per unit volume. The pressure of vapor in equilibrium with a liquid is called vapor pressure at that particular temperature. Vapor pressure is temperature dependent. At a given temperature each liquid has a characteristic vapor pressure depending on the strength of the intermolecular forces. Note: As long as liquid and vapor are present the pressure exerted by the vapor is independent of the volume of the container.
  30. 30. LIQUID-VAPOR EQUILIBRIUM Vaporization is the process in which a liquid is converted to a gas (referred as vapor). If the container is open evaporation proceeds until all the liquid is gone. However if the container is closed a dynamic equilibrium is established between the liquid and the vapor in which the rate of condensation equals the rate of vaporization. VAPOR LIQUID BROMINE CLOSED CONTAINER SAFETY CONTAINER
  31. 31. BOILING POINT The temperature at which a liquid boils depends on the pressure above it. A liquid boils at a temperature at which its vapor pressure is equal to the pressure above its surface. If this pressure is 1 atm (760 mm Hg) the temperature is referred to as the normal boiling point. The normal boiling point of water is 100 °C. The boiling point of a liquid can be reduced by applying vacuum.
  32. 32. If a substance has a high vapor pressure at room temperature, it is also likely to have a _______ boiling point because the vapor pressure of a liquid must _______ the atmospheric pressure in order for boiling to occur. 1. high; equal 2. high; surpass 3. low; equal 4. low; be lower than
  33. 33. Boling Point Temperature at which: vapor pressure of a liquid = atmospheric pressure.
  34. 34. Factors Affecting Boiling Point 1) Intermolecular forces Water (H20) MW = 18 amu Boiling point = 100° C Methane (CH4) MW = 16 amu Boiling point = -164° C 2) Number of sites for intermolecular interaction Methane (CH4) MW = 16 amu Boiling point = -164° C Weak London forces Weak London forces plus Strong hydrogen bonds Hexane (C6H14) MW = 86 amu Boiling point = 69° C Weak London forces Stronger London forces The more electrons in the molecule and the larger the area = stronger London forces
  35. 35. 3) Molecular shape Pentane (C5H12) MW = 72 amu Boiling point = 36.2 ° C 2,2-Dimethylpropane (C5H12) MW = 72 amu Boiling point = 9.5° C The larger the area the stronger the London forces
  36. 36. Solids Crystallization (solidificationCrystallization (solidification): When liquids are cooled, their molecules come close together, attractive forces between them become strong, random motion stops, and a solid is formed.
  37. 37. SOLIDS Virtually all substances that are gases or liquids at 25 C and 1 atm are molecular. Nonmolecular solids are classified in three groups (b, c, and d below). X = nonmetal M+ = metal X- = anion e- = electron DIAMOND TABLE SALT IRONSOLID I2 or WATER
  38. 38. IONIC SOLIDS The geometry of ionic crystals is more complex than that of metals. Packing can be visualized in terms of the cell units. Anions (larger size) are typically located at the corners and cations (smaller size) are distributed in the holes in between.
  39. 39. Liquid water Solid water MOLECULAR SOLIDS
  40. 40. Protein = chain of amino acids Carbohydrate = chain of sugars POLYMERIC SOLIDS
  41. 41. NETWORK SOLIDS Diamonds have a melting point above 3500 °C. In diamonds, each carbon atom forms single bonds with four other carbon atoms arranged tetrahedrally around it. The three dimensional covalent bonding contributes to the diamond unusual hardness.
  42. 42. NETWORK SOLIDS Graphite also has a melting point above 3500 °C. In graphite carbons are arranged in layers of hexagonal pattern. Each carbon is covalently bonded to three others (two by single bonds and one by double bond). The forces between adjacent layers of graphite are of the dispersion type (and weak). Layers
  43. 43. “Soot” is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon. AMORPHOUS SOLIDS Combustion pipe clogged with soot
  44. 44. “Buckyball” Carbon structure containing 60 carbons “Nanotube” Carbon tubular structure INTERESTING RECENTLY DISCOVERED FORMS OF CARBON 1996 Nobel prize
  45. 45. Phase Changes Phase change:Phase change: a change from one physical state (gas, liquid, or solid) to another. Phase:Phase: any part of a system that looks uniform throughout: ice, water, steam.
  46. 46. Phase Diagram
  47. 47. Which of the following processes takes the most energy? 1. Melting 50 g ice at 0°C 2. Boiling 50 g water at 100°C 3. Heating 50 g water from 0°C to 10°C 4. Heating 50 g steam from 100°C to 110°C

Notas del editor

  • Vapor pressure increases with temperature until it equals the atmospheric pressure.
  • High boiling compounds that might decompose or oxidize at its normal boiling point are distilled at reduced temperature under vacuum and then condensed.
  • Diamond 3820 degrees Kelvin
    Table salt melting point1074 K
    Iron 1808 K
    Iodine 386.5 K
    Water 373 K
  • Each oxygen atom in ice is surrounded tetrahedrally by four others. Hydrogen bonds link each pair of oxygen atoms. This arrangement of water molecules in ice creates a very open structure which accounts for the fact that ice is less dense than water at 0oC.
  • Diamond Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, clarity, color, and cut. The carat weight measures the mass of a diamond. One carat is defined as exactly 200 milligrams (about 0.007 ounce).
    Clarity is a measure of internal defects of a diamond called inclusions. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy. The number, size, color, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond.
    Color A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable.
    Cut.There are mathematical guidelines for the angles and length ratios at which the diamond is supposed to cut at in order to reflect the maximum amount of light.
    Cubic zirconia (or CZ) (diamond simulant) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4).
    Because of its low cost, durability, and close visual likeness to diamond, synthetic cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. The stabilizer is required for cubic crystal formation; it may be typically either yttrium or calcium oxide, the amount and stabilizer used depending on the many recipes of individual manufacturers. Therefore the physical and optical properties of synthesized CZ vary, all values being ranges.
  • A lead pencil contains a graphite rod, thin layer of which rub off onto the paper as we write