Gases, Liquids, and Solids

Transcription

1 Gases, Liquids, and Solids

2 Kinetic Molecular Theory Particles of matter are always in motion and this motion has consequences.

3 Liquids and Solids How are liquids and solids similar to and different from gases? (in terms of the KMT) Property Gases Liquids Solids Spacing Movement Avg. KE Attraction between particles Disorder/Order Volume Shape Fluidity Density Compressibility Diffusing Ability

4 Liquids and Solids Property Gases Liquids Solids Spacing Far apart much closer tog. than gases Movement Very fast slower, slip by each other most closely packed vibrate in position Avg. KE high lower lowest Attraction between particles Disorder Very low Highly disordered more effective, e.g. H-bonding less disordered (due to IM forces less mobility most effective, e.g. ionic bond most ordered Volume Indefinite definite (like solids) definite

5 Liquids and Solids Property Gases Liquids Solids Shape Indefinite Indefinite definite Fluidity Yes Yes (like gases) Density Very low Relatively high (closer to solids) 10% less than in their solid state Compressibility Very compressible (1000 X) Relatively incompressible (~ 4%), like solids) No (but some amorphous solids flow at a very slow rate, e.g. glasses) Highest more closely packed (osmium is the densest) less compressible than liquids

6 Liquids and Solids Property Gases Liquids Solids Diffusing Ability Very yes, but much slower than gases (closer tog., attractive forces get in the way; increased T increased diffusion) millions of times slower in solids than in liquids

7 Gases Chapters 13.1 and 14

8 Kinetic Molecular Theory (for gases) 1. Size Gases consist of large numbers of tiny particles, which have mass. The distance between particles is great. Gas particles are neither attracted to nor repelled by each other.

9 Kinetic Molecular Theory (for gases) Motion a) Gas particles are in constant, rapid, straightline, random motion. They possess KE. b) Gas particles have elastic collisions (with each other and container walls) (no net loss of KE) e.g. elastic : pool balls (do not lose KE) inelastic: car crash (lose lots of KE)

10 Kinetic Molecular Theory Energy 3. The average KE of the gas particles is directly proportional to the Kelvin temperature of the gas. (Reminder: KE = ½ mv 2 )

11 Properties of Gases very low density (1/1000 that of solids or liquids) indefinite volume, expand and contract fluid diffuse through each other have mass exert pressure 1 mol at STP = 22.4 L (STP = 273 K, 1 atm)

12 Effusion vs. Diffusion Effusion: escape rate of gas through a small opening Diffusion: one material moving through another gases diffuse through each other

13 Graham s Law The kinetic energies of any two gases at the same temperature are equal: recall KE = ½ mv 2 v a m b v b m a v = rate of diffusion (or effusion) m = molar mass (g/mol)

14 Graham s Law Rate of gas effusion is related to MM of gas KE= ½ mv 2 (m= molar mass, v=velocity (m/s) ) ½ m a v a2 = ½ m b v b 2

15 Practice Problems 1. The molar mass of gas "b" is g/mol and gas "a" is g/mol. If gas "b" is travelling at 5.25 x 10 9 m/s, how fast is gas "a" travelling? Both gases have the same KE. (3.17 x 10 9 m/s)

16 Practice Problems 2.An unknown gas effuses through an opening at a rate 3.53 times slower than nitrogen gas. What is the molecular mass of the unknown gas? (349 g/mol)

17 Forces of Attraction Bonding forces: Ionic, Metallic and Covalent Ionic and metallic bonding forces hold atoms of compounds together: Intramolecular forces (covalent bonds) hold atoms of individual molecules together: Intermolecular forces exist between molecules of covalently-bonded compounds - Relatively weak compared to intramolecular forces 3 types: Dispersion (London) forces Dipole-dipole forces Hydrogen bonds

18 London Forces (aka van der Waals or Dispersion forces) Weakest intermolecular force occurs between all molecules larger # of electrons larger temporary dipole stronger attractions between molecules higher m.p. and b.p. F 2 and Cl 2 are gases at room T Br 2 is liquid at room T (more electrons than F 2 and Cl 2 ) I 2 is solid at room T (largest number of electrons) London forces are the only intermolecular forces in the noble gases

19 Dipole Forces Attractions between polar molecules, stronger than London dispersion forces: (-) end of one polar molecule attracts the (+) end of another polar molecule more polar stronger dipole force closer together stronger dipole force

20 Hydrogen Bonding Always involves H attached to an O, F or N (small, high electronegativity) Strongest intermolecular force: 5% of the strength of a covalent bond! Increased b.p. and viscosity Accounts for high b.p. of H 2 O

21 Gas Pressure Pressure = Force/Area Units Force in N Pressure in: Pascals (N/m 2 ) Torr mm Hg atmospheres Standard Pressure kpa 760 torr 760 mm Hg 1 atm

22 Pressure = force area Units: Pascals: 1 Pa = 1 N/m 2, 1 kpa = 1000 Pa mm Hg (or Torr) psi = lbs/in 2 atm = atmospheres Standard sea level 1atm = kpa = 760. mm Hg = 760. Torr = 14.7 psi

23 Dalton s Law of Partial Pressures P total = P a + P b +

24 Dalton s Law Practice Problem A 1 L sample contains 78% N 2, 21% O 2 and 1.0% Ar. The sample is at a pressure of 1 atm (760. mm Hg). a) What is the partial pressure of each gas in mm Hg? b) What is the partial volume of each gas in ml?

25 Application of Dalton s Law Collecting gas by displacement of water P total = P gas + P H2 O P total = total pressure (given) P H2O varies at different temperatures (see table )

26 Collecting Gas by Water Displacement The gas bubbles through the water in the jar and collects at the top due to its lower density. The gas has water vapor mixed with it. P total = P gas + P H2O P dry gas = P total P H2O P total is what is measured (= atmospheric P) P H2O can be found in standard tables of vapor pressure of water at different temperatures

27 Vapor pressure of H 2 O at various temperatures P total = P gas + P H2 O Practice Problem: Hydrogen gas is collected over water at a total pressure of 95.0 kpa and temperature of 25 o C. What is the partial pressure of the dry hydrogen gas? (A: 91.8 kpa)

28 Mole Fraction mole fraction of gas A = moles of gas A total moles gas = P gas A P total 1. The partial pressure of oxygen was observed to be 156 torr in air with a total atmospheric pressure of 743 torr. Calculate the mole fraction of O 2 present. P O2 P total = 156 torr 743 torr = The partial pressure of nitrogen was observed to be 590 mm Hg in air with a total atmospheric pressure of 760. mm Hg. Calculate the mole fraction of N 2 present. P N2 P total = 590. mm Hg 760. mm Hg = 0.78

29 Partial Pressure problems 1. Determine the partial pressure of oxygen (O 2 ) collected over water if the temperature is 20.0 o C and the total (atmospheric) gas pressure is 98.0 kpa. (95.7 kpa) 2. The barometer at an indoor pool reads kpa. If the temperature in the room is 30.0 o C, what is the partial pressure of the dry air? ( kpa) 3. What is the mole fraction of hydrogen (H 2 ) in a gas mixture that has a P H2 of 5.26 kpa? The other gases in the mixture are oxygen (O 2 ), with a P O2 of 35.2 kpa and carbon dioxide with a P CO2 of 16.1 kpa. (0.0930)

30 Barometer instrument used to measure atmospheric P, using a column of Hg invented by Evangelista Torricelli in 1643

31 Manometer measures P of an enclosed gas relative to atmospheric P (open end) Gas P = atmospheric P ± P of liquid in U-tube Ask: Is the gas P higher or lower than atmospheric P? - If higher, add the pressure of the liquid to atm P. - If lower, subtract the pressure of the liquid from atm P.

32 Manometer practice problems

33 Manometer practice problems

34 Forces of Attraction Liquids and Solids Phase Changes

35 Phase Changes process Phases Involved Endo/Exothermic? melting solid liquid endothermic

36 Phase Changes process Phases Involved Endo/Exothermic? Melting Solid to liquid Endothermic Freezing Liquid to solid Exothermic Vaporization Liquid to gas Endothermic Condensation Gas to liquid Exothermic Sublimation Solid to gas Endothermic Deposition Gas to solid Exothermic

37 Phase Change Terminology Melting point (m.p.): T at which a solid becomes a liquid. Note: Amorphous solids act somewhat like liquids even when solid Vapor Pressure (VP): P exerted by a vapor over a liquid Boiling point (b.p.): T at which the VP of a liquid = atmospheric P Evaporation: Vaporization only at surface of liquid, below b.p. Freezing point: T at which liquid is converted into crystalline solid

38 Phase Diagrams Graph showing the relationships between solid, liquid and gaseous phases over a range of conditions, e.g. P vs. T Triple point = T and P conditions at which the solid, liquid and vapor of a substance can coexist at equilibrium Critical T = the highest T at which a gas can be liquified by P alone Critical P = P exerted by a substance at the critical T

39 Phase Diagrams

40 Phase Diagrams 1. What variables are plotted on a phase diagram? 2. How many phases of water are represented in its phase diagram? What are they? 3. What phases of water coexist at each point along the red curve? Along the yellow curve? 4. Look at the phase diagram for carbon dioxide. Above which a pressure and temperature is carbon dioxide unable to exist as liquid? 5. At which pressure and temperature do the solid, liquid, and gaseous phases of carbon dioxide coexist?

41 Phase Diagrams 1. What variables are plotted on a phase diagram? Pressure and temperature 2. How many phases of water are represented in its phase diagram? What are they? Three: solid, liquid, and vapor (gas) 3. What phases of water coexist at each point along the red curve? Solid and liquid along the yellow curve? Solid and gas 4. Look at the phase diagram for carbon dioxide. Above which pressure and temperature is carbon dioxide unable to exist as a liquid? 73 atm, 31 o C 5. At which pressure and temperature do the solid, liquid, and gaseous phases of carbon dioxide coexist? 5.1 atm, -57 o C

42 Phase Diagrams Temperature ( o C) Pressure (atm) Phase Liquid vapor

43 Phase Diagrams Temperature ( o C) Pressure (atm) Phase vapor -2 1 solid Liquid vapor liquid 0.00 < T < Liquid < 1.00 atm vapor

44 Gas vs. Vapor Gas Vapor State of particles at room temperature Gas formed from a substance that normally exists as a solid or liquid at room T and P Vaporization Conversion of a liquid to gas or vapor Boiling point T at which vapor pressure of liquid = atmospheric pressure

45 Boiling Point Boiling point at 1 atm = normal boiling point H 2 O enters vapor state within liquid. Vapor is less dense, rises to surface Needs constant energy (heat) to keep it boiling cooling process Liquid never rises above its boiling point! (at constant P) If atm P, less E is required for particles to escape atm P Mountains vs. pressure cooker

46 Evaporation Evaporation occurs when particles have enough KE to overcome their I.M. forces In a contained vessel (closed): dynamic equilibrium occurs when rate of vaporization = rate of condensation VP (which = partial pressure of a vapor above a liquid) depends on: 1. # gas particles: # particles vapor pressure 2. Temperature: as T v.p. (particles have more energy to escape) 3. Intermolecular forces: Stronger I.M. forces v.p. (fewer particles have enough energy to break the I.M. bonds and escape)

47

48 Evaporation In an uncontained vessel (open): evaporation is a cooling process: the most energetic particles leave so average KE of remaining particles is lower Rate of evaporation with in: T (more particles have energy to escape the liquid) air currents surface area

49 Evaporation vs. Boiling Evaporation takes place at liquid surface below boiling T Boiling occurs throughout liquid at boiling T

50 Liquids Viscosity: a measure of resistance to flow. In liquids, viscosity is determined by Intermolecular forces more attractions greater viscosity Molecular shape longer chains greater viscosity Temperature colder temp greater viscosity Surface tension: E required to increase the SA of a liquid by a given amount Stronger intermolecular forces greater surface tension Surfactants: compounds that lower the surface tension of water (e.g. detergent or soap)

51 Liquids Capillary action the result of cohesion and adhesion Cohesion = force of attraction between identical molecules Adhesion = force of attraction between different types of molecules e.g. Water in capillary tube adhesion between water molecules and glass > cohesion between water molecules

52 Solids Density of solids is higher than density of most liquids, and may be Crystalline or Amorphous Crystalline solids Made of crystals: particles arranged in orderly, geometric, repeating patterns Have definite geometric shape Crystal lattice = total 3-D array of points that describe the arrangements of particles, smallest unit is the unit cell Crystal has same symmetry as its unit cell Abrupt melting point - all bonds break at once

53 Crystalline Solids 7 shapes, based on arrangement of atoms in unit cell, cell lengths and cell angles:

54 Categories of Crystalline Solids 1. Atomic (e.g. noble gases) 2. Molecular (e.g. table sugar, proteins) 3. Covalent network (e.g. diamond, quartz) 4. Ionic 4. Metallic

55 Binding Forces in Crystals (see Bonding notes) Atomic and Covalent molecular crystals Weak intermolecular forces, low m.p., easily vaporized, relatively soft, good insulators Covalent network (e.g. diamond, graphite) 3-D covalent bonds (giant covalent molecules) very hard, brittle, high m.p., nonconductors or semiconductors; some are planar, e.g. graphite in sheets Ionic (e.g. NaCl) strong positive and negative ions, electrostatically attracted to one another hard, brittle, high m.p., good insulators Metallic (metals) positive ions surrounded by a cloud of electrons (electrons can move freely through lattice) high electrical conductivity, malleability, ductility

56 Amorphous solids Glasses and plastics particles arranged randomly nearly any shape, depending on molding No definite melting point, gradually soften to thick, sticky liquids Cool too fast for crystals to form

57 Describing Gases To describe a gas, you need: Volume Pressure Temperature (K) # particles (moles) Gas Laws

58 Constant Temperature What happens to P when V decreases? Constant Pressure What happens to V when T increases? Constant Volume What happens to P when T increases?

59 Constant Volume and Temperature What happens to P when the # of particles is increased? Constant Temperature and Pressure What happens to V when the # of particles is increased?

60 The Combined Gas Law What happens to a gas when various conditions are changed? P 1 V 1 T 1 = P 2V 2 T 2 The combined gas law includes Boyle s, Charles s, and Gay-Lussac s Laws.

61 Boyle s Law (constant T) P 1 V 1 = P 2V 2 P 1 V 1 =P 2 V 2 T 1 T 2 Demonstrates an inverse relationship between pressure and volume:

62 Charles s Law (constant P) P 1 V 1 = P 2V 2 V 1 = V 2 T 1 T 2 T 1 T 2 Demonstrates a direct relationship between temperature and volume:

63 Gay Lussac s Law (constant V) P 1 V 1 = P 2V 2 P 1 = P 2 T 1 T 2 T 1 T 2 Demonstrates a direct relationship between temperature and pressure

64 Boyle's Law P 1 V 1 = P 2 V 2 The pressure on 2.50 L of anaesthetic gas is changed from 760. mm Hg to 304 mm Hg. What will be the new volume if the temperature remains constant? (6.25 L)

65 Charles's Law V 1 = V 2 T 1 T 2 If a sample of gas occupies 6.8 L at 327 o C, what will be its volume at 27 o C if the pressure does not change? (3.4 L)

66 Gay-Lussac's Law P 1 = P 2 T 1 T 2 A gas has a pressure of 50.0 mm Hg at 540. K. What will be the temperature, in o C, if the pressure is 70.0 mm Hg and the volume does not change? (483 o C)

67 Combined Gas Law P 1 V 1 = P 2 V 2 T 1 T 2 1. If a gas has a pressure of 2.35 atm at 25 o C, and fills a container of 543 ml, what is the new pressure if the container is increased to 750. ml at 50.1 o C? (1.84 atm)

68 Combined Gas Law 2. A sample of methane that initially occupies 250. ml at 500. Pa and 500. K is expanded to a volume of 700. ml. To what temperature will the gas need to be heated to lower the pressure of the gas to 200. Pa? (560. K)

69 Ideal Gases Real Gases Based on kinetic molecular theory Because particles of real gases occupy space: Follows gas laws at all T and P Follow gas laws at most T and P Assumes particles: - have no V impossible At high P, individual volumes count - have no attraction to each other At low T, attractions count if true, would be gases impossible to liquefy (e.g. CO 2 is liquid The more polar the molecule, the more attraction counts P decreases at 5.1 atm, < 56.6 o C

70 The Ideal Gas Law: PV = nrt To describe a gas completely you need to identify: V Volume P Pressure T Temperature in K n - # of moles The Ideal Gas Law: n mass molar mass m M g g mol 1. Can be used to derive the combined gas law moles 2. Is usually used to determine a missing piece of information about a gas (requires the ideal gas constant R)

71 Ideal Gas Law Most gases act like ideal gases most of the time. PV = nrt P, V inversely related BOYLE PT directly related GAY-LUSSAC V, T directly related CHARLES V, n directly related AVOGADRO R = universal gas constant

72 R: The Ideal Gas Constant Derived from ideal gas law using STP conditions: standard temperature: 273K standard pressure: 1 atm volume of 1 mole of gas: 22.4 L PV = nrt R = PV nt 1 atm 22.4 L = 1 mol 273 K L atm K mol The value of R depends on units of pressure used: L kpa 62.4 L mm Hg K mol K mol

73 Ideal Gas Law Solve for R at STP: T = 0 o C = 273 K; P = 1 atm R = PV = (1 atm)(22.4 L) = L atm nt (1 mol)(273 K) mol K Note that the value of R depends on the units of pressure

74 Ideal Gas Law Calculate the pressure, in atmospheres, of 1.65 g of helium gas at 16.0 o C and occupying a volume of 3.25 L. P =? PV = nrt V = 3.25 L n = 1.65 g (1 mol He) = mol He 4.00 g He R = L atm/mol K T = 16.0 o C = 289 K P = nrt = (0.412 mol)( L atm)(289 K) V 3.25 L mol K = 3.01 atm

75 Combined Gas Law Warmup 4. The volume of a gas-filled balloon is 30.0 L at 40 o C and 153 kpa. What volume will the balloon have at STP? (A: 39.5 L) 5. A 3.50-L gas sample at 20 o C and a pressure of 86.7 kpa expands to a volume of 8.00 L. The final pressure of the gas is 56.7 kpa. What is the final temperature of the gas, in o C? (A: 165 o C, 438 K)

76 Ideal Gas Law Practice 1. A sample of carbon dioxide with a mass of g was placed in a 350. ml container at 127 o C. What is the pressure, in kpa, exerted by the gas? (53.9 kpa)

77 Ideal Gas Law Practice 2. A 500. g block of dry ice (solid CO 2 ) vaporizes to a gas at room temperature. Calculate the volume of gas produced at 25 o C and 975 kpa. (29.0 L CO 2 )

78 Ideal Gas Law Practice 3. At what temperature will 7.0 mol of helium gas exert a pressure of 1.2 atm in a 25.0 kl tank? (5.2 x 10 4 K)

79 Ideal Gas Law Practice 4. What mass of chlorine (Cl 2 ) is contained in a 10.0 L tank at 27 o C and 3.50 atm? Hint: begin by solving for n. (101 g)

80 Density of Gases Measured in g/l (liquids and solids: g/ml) 1 mole of any gas = 22.4 L at STP (273 K and 1 atmosphere) You can use 22.4 L = 1 mol as a conversion factor at STP For non-standard conditions, use the ideal gas law.

81 Finding Molar Mass of a Gas Using Its Density, at STP 1. What is the molar mass of a gas that has a density of 1.28 g/l at STP? (28.7 g/mol) 2. A g gas sample is found to have a volume of 200. ml at STP. What is the molar mass of this gas? (58.1 g/mol) 3. A chemical reaction produced 98.0 ml of sulfur dioxide gas (SO 2 ) at STP. What was the mass (in grams) of the gas produced? (0.280 g SO 2 )

82 Finding Molar Mass of a Gas Using the Ideal Gas Law under nonstandard A 1.25 g sample conditions of the gaseous product of a chemical reaction was 4. found to have a volume of 350. ml at 20.0 o C and 750. mm Hg. What is the molar mass of this gas? 2 steps 1. Find the number of moles (n), using the Ideal Gas Law 2. Divide the mass of the gas given in the problem by n g/mol (86.8 g/mol) (More practice Gases WS #5)

83 Density of Gases (Honors) Practice: 1. Derive density from the ideal gas law (RQ 14.3): PV = nrt n = m/mm 2. Rearrange to isolate M (molar mass) Apply these variations to HW on p. 438, #46-50

84 Warmup 1. a) What is the density of a gas that has a mass of g and a volume of 178 ml? (A: 1.44 x 10-1 g/l or 1.44 x 10-4 g/ml) b) If this is the density under STP, what is the molar mass of this gas? (A: 3.22 or 3.23 g/mol) 2. What is the molar mass of a gas that has a mass of 1.23 g and a volume of 580. ml at STP? (A: 47.5 g/mol) 3. What is the molar mass of a gas that has a mass of 1.53 g and volume of 825 ml at 55 o C and 95 kpa? (A: 53 g/mol)

85 Stoichiometry and Gases at STP Calcium carbonate reacts with phosphoric acid to produce calcium phosphate, carbon dioxide, and water. (review) 3 CaCO 3(s) + 2 H 3 PO 4(aq) Ca 3 (PO 4 ) 2(aq) + 3 CO 2(g) + 3 H 2 O (l) 1. How many grams of phosphoric acid, H 3 PO 4, react with excess calcium carbonate, CaCO 3, to produce 3.74 g of Ca 3 (PO 4 ) 2? (2.36 g H 3 PO 4 ) 2. Assuming STP, how many liters of carbon dioxide are produced when 5.74 g of H 3 PO 4 reacts with an excess of CaCO 3? (1.97 L)

86 Stoichiometry of Gases non-stp conditions Context is stoichiometry To get to moles of your known asap, you either perform a mass conversion, or use PV=nRT solve for # moles The last step of stoich is to convert moles of your unknown into required units. That means either moles mass or volume, for which you use PV=nRT solves for L

87 Stoichiometry and Gases under non-stp Conditions Either stoichiometry first (known = solid or liquid) to find moles of unknown, followed by the Ideal Gas Law to find the volume of a gaseous product (unknown), OR use the Ideal Gas Law to find the # moles of a gaseous reactant (known), followed by stoichiometry to find the amount of a solid or liquid product (unknown).

88 Stoichiometry and Gases under non-stp Conditions If water is added to magnesium nitride, ammonia gas is produced when the mixture is heated. Mg 3 N 2(s) + 3 H 2 O (l) 3 MgO (s) + 2 NH 3(g) 1. If 10.3 g of magnesium nitride is treated with water, what volume of ammonia gas would be collected at 24 o C and 752 mm Hg? (A: 5.03 L) 2. When you produce 16.2 L of ammonia gas at 100. o C and 802 mm Hg, how many grams of magnesium oxide are also produced? (A: 33.7 g MgO)

89 Warm up Stoichiometry and Gases at STP The formation of aluminum oxide from its constituent elements is represented by this equation. 4 Al (s) + 3 O 2(g) 2 Al 2 O 3(s) 1. How many grams of aluminum are required to react with excess oxygen, to produce 3.74 g of Al 2 O 3? (1.98 g Al) 2. Assuming STP, how many liters of oxygen are produced when 5.74 g of Al 2 O 3 reacts with an excess of aluminum? (1.89 L O 2 )

90 Warmup - Stoichiometry and Gases at STP If 650. ml of hydrogen gas is produced through a replacement reaction involving solid iron and sulfuric acid (H 2 SO 4 ) at STP, how many grams of iron (II) sulfate are also produced?

91 Stoichiometry and Gases non-stp conditions How many liters of oxygen at 27 o C and 188 mm Hg are needed to burn 65.5 g of carbon according to the equation 2 C (s) + O 2(g) 2 CO (g) (A: 272 L)

92 Stoichiometry and Gas Laws non-stp conditions 23. From Gases WS #6: WO 3 (s) + 3 H 2 (g) W (s) + 3 H 2 O (l) How many liters of hydrogen at 35 o C and 745 mm Hg are needed to react completely with 875 g of tungsten oxide? Begin with stoich or PV = nrt? (A:292 L)

93 Stoichiometry and Gas Laws non-standard conditions 24. Magnesium will burn in carbon dioxide to produce elemental carbon and magnesium oxide. What mass of magnesium will react with a 250 ml container of CO 2 at 77 o C and 65 kpa? Begin with stoich or PV=nRT? (A: 0.27 g Mg)

94 Summary of Gas Laws (check your reference sheet 1 st page of notes) Grahams Law Dalton s Law v a v b m b m a P total = P a + P b + P c... P n Ideal Gas Law Combined Gas Law Boyle s Law (on top) Charles s Law (likes T.V.) Gay Lussac s Law (what s left ) PV nrt P 1 V 1 T 1 P 2V 2 T 2 P 1 V 1 P 2 V 2 V 1 T 1 V 2 T 2 P 1 T 1 P 2 T 2

95 Vapor Pressure What is the VP of ethanol at 60 o C? of water at the same T (60 o C)? Which compound boils at a lower T? How can you tell? Which exhibits stronger IMFs? ethanol or water? Explain your answer.

96 Vapor Pressure What is the VP of ethanol at 60 o C? about 402 torr of water at the same T (60 o C)? about 180 torr Which compound boils at a lower T? How can you tell? Which exhibits stronger IMFs? ethanol or water?

97

98 Warmup Stoichiometry and Gases 1. The formation of aluminum oxide from its constituent elements is represented by this equation. 4 Al (s) + 3 O 2(g) 2 Al 2 O 3(s) Assuming STP, how many liters of oxygen are produced from 5.74 g of Al 2 O 3? (1.89 L O 2 ) 2. Consider the following chemical equation: 2 Cu 2 S (s) + 3 O 2(g) 2 Cu 2 O (s) + 2 SO 2(g) What volume of oxygen gas, measured at 27 o C and atm, is required to react completely with 25.0 g of copper(i) sulfide? (A: 5.82 L O 2 ) 3. What mass of NaCl can be produced by the reaction of Na (s) with 3.65 L Cl 2(g) at 25 o C and 105 kpa? (Hint: Write the chemical equation first.) (A: 18.1 g NaCl)

99 Gas Stoichiometry Volume volume: Since all gases take up the same volume at the same temperature, the mole ratio can be used as a volume ratio of two gases in the equation. Volume mass: Requires conditions under which reaction takes place - use ideal gas law.