Chapter 11. Liquids and Intermolecular Forces

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1 Chapter 11 Liquids and Intermolecular Forces

2 States of Matter The three states of matter are 1) Solid Definite shape Definite volume 2) Liquid Indefinite shape Definite volume 3) Gas Indefinite shape Indefinite volume 2015 Pearson Education, 2

3 States of Matter Main difference between states of matter is the strength of the intermolecular forces of attraction Stronger forces bring molecules closer together Solids and liquids known as the condensed phases 2015 Pearson Education, 3

4 CHARACTERISTICS OF STATE OF MATTER 4

5 Characteristics of State of Matter: Solid Retains own shape and volume Does not expand to fill its container Virtually incompressible Does not flow Diffusion within a solid occurs extremely slowly 5

6 Characteristics of State of Matter: Liquid Assumes shape of portion of container it occupies Does not expand to fill its container Is virtually incompressible Flows readily Diffusion within a liquid occurs slowly 6

7 Characteristics of State of Matter: Gas Assumes both volume and shape of its container Expands to fill its container Is compressible Flows readily Diffusion within a gas occurs rapidly 7

8 State of Matter What state of matter will a substance take? The answer to this question largely relies on the Balance between the kinetic energies of the particles Forces of attraction between the molecules Kinetic energy is the energy an object posses due to its motion 8

9 State of Matter What state of matter will a substance take? The answer to this question largely relies on the Balance between the kinetic energies of the particles Forces of attraction between the molecules Kinetic energy is the energy an object posses due to its motion 2015 Pearson Education, 9

10 Forces of attraction between the molecules INTERMOLECULAR FORCES 10

intermolecular forces Intermolecular forces affect boiling points,

11 Intermolecular Forces Intermolecular forces are attractive forces between molecules Intramolecular attractions (bonds) are stronger than intermolecular forces Intermolecular forces affect boiling points, melting points, viscosity, surface tension, and capillary action 2015 Pearson Education, 11

12 Types of Intermolecular Force Types of intermolecular forces (weakest to strongest forces): 1. Dispersion forces (or London dispersion forces) 12

13 Dispersion Forces London dispersion forces Weak temporary dipole-dipole interaction between an atoms or molecules Tendency of an electron cloud to distort is called polarizability 2015 Pearson Education, 13

Dispersion Forces Factors affect dispersion force Number of electrons in an atom More electrons, more dispersion force Larger diameter atoms or

14 Dispersion Forces Factors affect dispersion force Number of electrons in an atom More electrons, more dispersion force Larger diameter atoms or molecules more susceptible to polarization Shape of molecules with similar masses More compact, less dispersion force 2015 Pearson Education, 14

15 Dispersion Forces: Boiling Point Ease of polarization increases With molecular weight Boiling point Intermolecular force (force between molecules) 2015 Pearson Education, 15

16 List the substances CCl 4, CBr 4, and CH 4 in order of increasing boiling point. a. CH 4 < CBr 4 < CCl 4 b. CCl 4 < CH 4 < CBr 4 c. CH 4 < CCl 4 < CBr 4 d. CBr 4 < CCl 4 < CH 4 16

17 List the substances CCl 4, CBr 4, and CH 4 in order of increasing boiling point. a. CH 4 < CBr 4 < CCl 4 b. CCl 4 < CH 4 < CBr 4 c. CH 4 < CCl 4 < CBr 4 d. CBr 4 < CCl 4 < CH 4 17

18 Types of Intermolecular Force Types of intermolecular forces (weakest to strongest forces): 1. Dispersion forces (or London dispersion forces) 2. Dipole dipole forces 18

19 Dipole Dipole Interactions Dipole-dipole interaction Intermolecular attractive force between polar molecules Polar molecules have a more positive and a more negative end Oppositely charged ends attract each other 2015 Pearson Education, 19

20 Dipole Dipole Interactions Dipole-dipole interaction Intermolecular attractive force between polar molecules Polar molecules have a more positive and a more negative end Oppositely charged ends attract each other 2015 Pearson Education, 20

21 Dipole Dipole Interactions Molecules of approximately equal mass and size, the more polar the molecule, the higher its boiling point 2015 Pearson Education, 21

22 Will dipole-dipole interactions or dispersion forces be the dominating force if both are possible? Molecules of comparable size and shape Dipole dipole interactions will likely be the dominating force One molecule is much larger than another Dispersion forces will likely determine its physical properties 22

23 Types of Intermolecular Force Types of intermolecular forces (weakest to strongest forces): 1. Dispersion forces (or London dispersion forces) 2. Dipole dipole forces 3. Hydrogen bonding (a special dipole dipole force) 23

24 Hydrogen Bonding Hydrogen bonding Dipole-dipole interaction Unusually strong Occurs between highly electronegative atom and a hydrogen atom bonded to a highly electronegative atom (N, O or F) 2015 Pearson Education, 24

25 What Causes Hydrogen Bonds? Hydrogen bonding arises from high electronegativity of nitrogen, oxygen, and fluorine Atoms interact with a nearly bare nucleus of hydrogen (which contains one proton) 2015 Pearson Education, 25

26 Types of Intermolecular Force Types of intermolecular forces (weakest to strongest forces): 1. Dispersion forces (or London dispersion forces) 2. Dipole dipole forces 3. Hydrogen bonding (dipole dipole force) 4. Ion dipole forces 26

27 Ion Dipole Interactions Ion dipole interactions Attractive force between an ion and a polar molecule Found in solutions of ions Enables ionic substances to dissolve in polar solvents 2015 Pearson Education, 27

28 In which mixture do you expect to find ion dipole forces between solute and solvent? CH 3 OH in water or Ca(NO 3 ) 2 in water. a. CH 3 OH in water, because CH 3 OH is a strong electrolyte and forms ions. b. Ca(NO 3 ) 2 in water, because Ca(NO 3 ) 2 is a strong electrolyte and forms ions. c. CH 3 OH in water, because CH 3 OH is a weak electrolyte and forms ions. d. Ca(NO 3 ) 2 in water, because Ca(NO 3 ) 2 is a weak electrolyte and forms ions. 28

29 In which mixture do you expect to find ion dipole forces between solute and solvent? CH 3 OH in water or Ca(NO 3 ) 2 in water. a. CH 3 OH in water, because CH 3 OH is a strong electrolyte and forms ions. b. Ca(NO 3 ) 2 in water, because Ca(NO 3 ) 2 is a strong electrolyte and forms ions. c. CH 3 OH in water, because CH 3 OH is a weak electrolyte and forms ions. d. Ca(NO 3 ) 2 in water, because Ca(NO 3 ) 2 is a weak electrolyte and forms ions. 29

30 Types of Intermolecular Force Types of intermolecular forces (weakest to strongest forces): 1. Dispersion forces (or London dispersion forces) 2. Dipole dipole forces 3. Hydrogen bonding (dipole dipole force) 4. Ion dipole forces Note: The first two types are also referred to collectively as van der Waals forces 30

31 What major type of attractive interaction must be overcome for water to evaporate? a. Hydrogen bonding b. Dispersion forces c. Covalent bonds d. Dipole-dipole forces 31

32 What major type of attractive interaction must be overcome for water to evaporate? a. Hydrogen bonding b. Dispersion forces c. Covalent bonds d. Dipole-dipole forces 32

33 Liquid Properties Affected by Intermolecular Forces Boiling point Melting point Viscosity Surface tension Capillary action

Increases with stronger intermolecular forces

34 Viscosity Viscosity Resistance of a liquid to flow Related to ease which molecules move past each other Increases with stronger intermolecular forces Decreases with higher temperature 2015 Pearson Education, 34

Surface Tension Surface tension Measure inward force on the surface of a liquid Water molecules Within the body Forces acting on molecules cancel out At the surface

35 Surface Tension Surface tension Measure inward force on the surface of a liquid Water molecules Within the body Forces acting on molecules cancel out At the surface There is a net inward force» No attractive force from above» Molecules on the surface contract and resist being stretched or broken Surface acts like thin elastic sheet 35

36 Surface Tension Surface tension Measure inward force on the surface of a liquid Water molecules Within the body Forces acting on molecules cancel out At the surface There is a net inward force» No attractive force from above» Molecules on the surface contract and resist being stretched or broken Surface acts like thin elastic sheet 36

37 Surface Tension Surface tension Measure inward force on the surface of a liquid Water molecules Within the body Forces acting on molecules cancel out At the surface There is a net inward force» No attractive force from above» Molecules on the surface contract and resist being stretched or broken Surface acts like thin elastic sheet 2015 Pearson Education, Inc. 37

38 Important forces in capillary action Cohesive forces Capillary Action Intermolecular forces that bind similar molecules to one another Adhesive Forces Intermolecular forces that bind a substance to a surface 38

Capillary Action Capillary action Rise of liquids up narrow tubes Adhesive forces attract liquid to the wall of the tube Cohesive forces attract the liquid to

39 Capillary Action Capillary action Rise of liquids up narrow tubes Adhesive forces attract liquid to the wall of the tube Cohesive forces attract the liquid to itself Meniscus shape Stronger adhesive force Stronger cohesive force adhesive > cohesive cohesive > adhesive 39

40 PHASE CHANGES 40

41 Phase Changes Phase change Conversion from one state of matter to another Energy is either added or released 41

42 Phase Changes Phase change Conversion from one state of matter to another Energy is either added or released 2015 Pearson Education, Inc. 42

43 Phase Changes Heat of fusion Energy required to change 1 g of a solid at its melting point to a liquid Endothermic Heat is absorbed H fus = heat absorbed / g Units are J/g Has a positive charge 43

44 Phase Changes Heat of vaporization Energy required to change 1 g of a liquid at its boiling point to a gas Endothermic Heat is absorbed H vap = heat absorbed / gram Units are J/g Has a positive charge 44

45 Phase Changes Heat of sublimation Energy required to change 1 g of a solid directly to a gas Endothermic Heat is absorbed H sub = H fus + H vap Units are J/g Has a positive charge 45

heat added Within a phase Heat is the product of specific heat, sample mass, and temperature

46 Phase Changes Heating Curves Diagram of state of matter at different temperatures Plot of temperature vs. heat added Within a phase Heat is the product of specific heat, sample mass, and temperature change q = C s x m x T Phase Change Temperature of the substance does not change Heat is the product of mass and the heat of fusion or vaporization q = m x H 2015 Pearson Education, Inc. 46

47 Example: Heat Energy Calculate the heat change upon converting 1.00 mol of ice at -25 o C to water vapor (steam) at 125 o C under a constant pressure of 1 atm. The specific heats of ice, water, and steam are 2.09 J/g-K, 4.18 J/g-K, and 1.84 J/g-K, respectively. For H 2 O heat of fusion = 6.01 kj/mol and heat of vaporization = kj/mol. Analyze the question (information given): The goal is to calculate the total heat required to convert 1 mol of ice at -25 o C to steam at 125 o C. 47

48 Example: Heat Energy Plan: You can calculate the heat change for each segment on a heat curve for water and sum them to get the total heat change. Solve: For segment AB, enough heat is added to ice to increase its temperature by 25 o C. A temperature change of 25 o C is the same as a temperature change of 25 K. Use specific heat of ice to calculate the heat added at this time Pearson Education, Inc. 48

49 Example: Heat Energy Solve: AB: q = C s x m x T C s = 2.09 J/g-K; T = 25 K m =? Amount of substance = 1.00 mol q = (moles of substance) (molar mass) (specific heat) (temperature change) heat absorbed = (1.00 mol) (18.0 g/mol) (2.09 J/g-K) (25 K) = 940 J = 0.94 kj 2015 Pearson Education, Inc. 49

50 Example: Heat Energy Solve: For segment BC, in which ice is converted to water at 0 o C, use molar heat of fusion directly Molar heat of fusion = 6.01 kj/mol Moles = 1.00 mol q = molar heat of fusion x moles q = (6.01 kj/mol) (1.00 mol) = 6.01 kj 2015 Pearson Education, Inc. 50

51 Example: Heat Energy Solve: For segment CD, enough heat is added to liquid water to increase its temperature by 100 o C. A temperature change of 100 o C is the same as a temperature change of 100 K. Use specific heat of water to calculate the heat added at this time. q = (moles of substance) (molar mass) (specific heat) (temperature change) heat absorbed = (1.00 mol) (18.0 g/mol) (4.18 J/g-K) (100 K) = 7520 J = 7.52 kj 2015 Pearson Education, Inc. 51

52 Example: Heat Energy Solve: For segment DE, in which water is converted to liquid at 100 o C, use molar heat of vaporization directly Molar heat of vaporization = kj/mol Moles = 1.00 mol q = molar heat of vaporization x moles q = (40.67 kj/mol) (1.00 mol) = 40.7 kj 2015 Pearson Education, Inc. 52

53 Example: Heat Energy Solve: For segment EF, enough heat is added to steam to increase its temperature by 25 o C. A temperature change of 25 o C is the same as a temperature change of 25 K. Use specific heat of steam to calculate the heat added. q = (moles of substance) (molar mass) (specific heat) (temperature change) heat absorbed = (1.00 mol) (18.0 g/mol) (1.84 J/g-K) (25 K) = 830 J = 0.83 kj 2015 Pearson Education, Inc. 53

54 Example: Heat Energy Solve: The total heat absorbed is the sum of the changes of the individual steps Total heat absorbed = AB heat absorbed + BC heat absorbed + CD heat absorbed + DE heat absorbed + EF heat absorbed Total heat absorbed = 0.94 kj kj kj kj kj = 56.0 kj 2015 Pearson Education, Inc. 54

55 Example: Heat Energy Check: Compare the lengths of the horizontal segments with the value of the individual component to determine if results are reasonable. Notice the largest component is the heat of vaporization. AB heat absorbed = 0.94 kj BC heat absorbed = 6.01 kj CD heat absorbed = 7.52 kj DE heat absorbed = 40.7 kj EF heat absorbed= 0.83 kj 2015 Pearson Education, Inc. 55

56 VAPOR PRESSURE 56

increase increases the number of molecules that can escape

57 Vapor Pressure Some molecules have energy to escape the surface of the liquid at any temperature Temperature increase increases the number of molecules that can escape the liquid to become a gas (vapor) d 2015 Pearson Education, Inc. 57

equilibrium state Liquid molecules evaporate and vapor

58 Vapor Pressure Vapor pressure Pressure of a vapor in contact with its liquid Liquid and vapor reach a state of equilibrium state Liquid molecules evaporate and vapor molecules condense at the same rate 2015 Pearson Education, Inc. 58

Vapor Pressure Boiling point Temperature at which vapor pressure equals atmospheric pressure Liquid to gas conversion occurs in body of liquid Normal boiling

59 Vapor Pressure Boiling point Temperature at which vapor pressure equals atmospheric pressure Liquid to gas conversion occurs in body of liquid Normal boiling point Temperature at which boiling occurs at vapor pressure is 760 torr 59

60 Vapor Pressure Boiling point Temperature at which vapor pressure equals atmospheric pressure Liquid to gas conversion occurs in body of liquid Normal boiling point Temperature at which boiling occurs at vapor pressure is 760 torr 2015 Pearson Education, Inc. 60

61 When water boils, what are the bubbles composed of? a. Oxygen b. Water c. Carbon dioxide d. Other impurities 61

62 When water boils, what are the bubbles composed of? a. Oxygen b. Water c. Carbon dioxide d. Other impurities 62

63 PHASE DIAGRAMS 63

64 Phase Diagram Phase diagram Graph of pressure vs. temperature for a substance Shows melting, boiling, and sublimation points at different pressures 2015 Pearson Education, Inc. 64

65 Phase Diagram Phase diagram illustrates Gases liquefies under high pressure Triple point Temperature and pressure where 3 phases are in equilibrium 2015 Pearson Education, Inc. 65

66 Phase diagram illustrates Critical point Phase Diagram Pressure and temperature where distinctions between phases cease to exist Critical temperature: Highest temperature a liquid can exist Critical pressure: Pressure needed to compress liquid at T c 2015 Pearson Education, Inc. 66

67 Phase Diagram Phase diagram illustrates Critical point Supercritical fluid Liquid and gas phase are indistinguishable from each other State beyond critical temperature 2015 Pearson Education, Inc. 67

68 Why are the critical temperature and pressure for H 2 O so much higher than those for H 2 S, a related substance (Table 11.6)? a. The mass difference between H 2 S and H 2 O b. H 2 S makes strong hydrogen bonds. c. H 2 O makes strong hydrogen bonds. 68

69 Why are the critical temperature and pressure for H 2 O so much higher than those for H 2 S, a related substance (Table 11.6)? a. The mass difference between H 2 S and H 2 O b. H 2 S makes strong hydrogen bonds. c. H 2 O makes strong hydrogen bonds. 69

70 70

71 Which combination of kinetic energy (KE) and intermolecular forces (IF) results in formation of a solid? a. KE much less than IF b. KE much greater than IF c. KE and IF comparable, and very large d. KE and IF comparable, and very small 71

72 Which combination of kinetic energy (KE) and intermolecular forces (IF) results in formation of a solid? a. KE much less than IF b. KE much greater than IF c. KE and IF comparable, and very large d. KE and IF comparable, and very small 72

73 Which force below is the strongest intermolecular attractive force? a. Hydrogen bonding b. Ion-dipole forces c. Dipole-dipole forces d. London dispersion forces 73

74 Which force below is the strongest intermolecular attractive force? a. Hydrogen bonding b. Ion-dipole forces c. Dipole-dipole forces d. London dispersion forces 74

75 Which force below increases in strength as the molecular weight of the compound increases? a. Hydrogen bonding b. Ion-dipole forces c. Dipole-dipole forces d. London dispersion forces 75

76 Which force below increases in strength as the molecular weight of the compound increases? a. Hydrogen bonding b. Ion-dipole forces c. Dipole-dipole forces d. London dispersion forces 76

77 Which compound below is not capable of forming hydrogen bonds? a. CH 4 b. NH 3 c. H 2 O d. HF 77

78 Which compound below is not capable of forming hydrogen bonds? a. CH 4 b. NH 3 c. H 2 O d. HF 78

79 Which property is not affected by intermolecular forces? a. boiling point b. color c. melting point d. viscosity 79

80 Which property is not affected by intermolecular forces? a. boiling point b. color c. melting point d. viscosity 80

81 The ease of changing the charge distribution in a molecule is called its. a. conductivity b. solubility c. polarizability d. viscosity 81

82 The ease of changing the charge distribution in a molecule is called its. a. conductivity b. solubility c. polarizability d. viscosity 82

83 Which compound below has the highest boiling point? a. H 2 O b. H 2 S c. H 2 Se d. H 2 Te 83

84 Which compound below has the highest boiling point? a. H 2 O b. H 2 S c. H 2 Se d. H 2 Te 84

85 Which element below has the highest boiling point? a. Kr b. F 2 c. Cl 2 d. Br 2 85

86 Which element below has the highest boiling point? a. Kr b. F 2 c. Cl 2 d. Br 2 86

87 Which substance below has a greater density in its liquid state than in its solid state? a. iron b. glass c. water d. carbon dioxide 87

88 Which substance below has a greater density in its liquid state than in its solid state? a. iron b. glass c. water d. carbon dioxide 88

89 The resistance of a liquid to flow is called the of the liquid. a. density b. viscosity c. potential energy d. flow rate 89

90 The resistance of a liquid to flow is called the of the liquid. a. density b. viscosity c. potential energy d. flow rate 90

91 The energy required to convert a liquid to a vapor is called the of the liquid. a. boiling point b. freezing point c. heat of vaporization d. heat of fusion 91

92 The energy required to convert a liquid to a vapor is called the of the liquid. a. boiling point b. freezing point c. heat of vaporization d. heat of fusion 92

93 Isopropyl alcohol feels cool on the skin because it has an (X) heat of (Y). a. X = exothermic, Y = vaporization b. X = endothermic, Y = vaporization c. X = exothermic, Y = fusion d. X = endothermic, Y = fusion 93

94 Isopropyl alcohol feels cool on the skin because it has an (X) heat of (Y). a. X = exothermic, Y = vaporization b. X = endothermic, Y = vaporization c. X = exothermic, Y = fusion d. X = endothermic, Y = fusion 94

95 When heat is added to ice at zero degrees Celsius, what will happen? a. The temperature will increase. b. The temperature will decrease. c. The temperature will not change. d. A supercritical fluid will form. 95

96 When heat is added to ice at zero degrees Celsius, what will happen? a. The temperature will increase. b. The temperature will decrease. c. The temperature will not change. d. A supercritical fluid will form. 96

97 The highest temperature at which a substance can exist in its liquid state is called its point. a. boiling b. freezing c. triple d. critical 97

98 The highest temperature at which a substance can exist in its liquid state is called its point. a. boiling b. freezing c. triple d. critical 98

99 The temperature and pressure at which all three phases exist simultaneously is called the point of a substance. a. boiling b. freezing c. triple d. critical 99

100 The temperature and pressure at which all three phases exist simultaneously is called the point of a substance. a. boiling b. freezing c. triple d. critical 100

101 At high altitudes, the boiling point of water is a. 100 degrees Celsius. b. greater than 100 degrees Celsius. c. less than 100 degrees Celsius. d. equal to its freezing point. 101

102 At high altitudes, the boiling point of water is a. 100 degrees Celsius. b. greater than 100 degrees Celsius. c. less than 100 degrees Celsius. d. equal to its freezing point. 102

103 Which quantity is not used in calculating the total energy involved in converting 50 g of ice at 0 C to water at 95 C? a. the mass of the sample b. the heat of fusion of ice c. the heat capacity of liquid water d. the heat of vaporization of water 103

104 Which quantity is not used in calculating the total energy involved in converting 50 g of ice at 0 C to water at 95 C? a. the mass of the sample b. the heat of fusion of ice c. the heat capacity of liquid water d. the heat of vaporization of water 104

105 The substance that would evaporate most easily is one with intermolecular forces and a molar mass. a. weak; large b. weak; small c. strong; large d. strong; small 105

106 The substance that would evaporate most easily is one with intermolecular forces and a molar mass. a. weak; large b. weak; small c. strong; large d. strong; small 106

107 Substance X has a boiling point of 150 degrees F and a freezing point of 15 degrees F. The condensation point of X a. is 150 degrees F. b. is 15 degrees F. c. is 165 degrees F. d. is 135 degrees F. 107

108 Substance X has a boiling point of 150 degrees F and a freezing point of 15 degrees F. The condensation point of X a. is 150 degrees F. b. is 15 degrees F. c. is 165 degrees F. d. is 135 degrees F. 108

Chemistry: The Central Science

Chemistry: The Central Science Fourteenth Edition Chapter 11 Liquids and Intermolecular Forces Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions