5 Ion-Ion InteractionsCoulomb’s law states that the energy (E) of the interaction between two ions is directly proportional to the product of the charges of the two ions (Q1 and Q2) and inversely proportional to the distance (d) between them.
6 Predicting Forces of Attraction Coulombs Law indicates the increases in the charges of ions will cause an increase in the force of attraction between a cation and an anion.Increases in the distance between ions will decrease the force of attraction between them.
8 Lattice Energy M+(g) + X-(g) ---> MX(s) The lattice energy (U) of an ionic compound is the energy released when one mole of the ionic compound forms from its free ions in the gas phase.M+(g) + X-(g) ---> MX(s)
9 Comparing Lattice Energies Lattice Energies of Common Ionic CompoundsCompoundU(kJ/mol)LiF-1047LiCl-864NaCl-790KCl-720KBr-691MgCl2-2540MgO-3791
10 Practice Determine which salt has the greater lattice energy. MgO and NaFMgO and MgS
12 Electron Affinity Cl(g) + e-(g) ---> Cl-(g) Electron affinity is the energy change occurring when one mole of electrons combines with one mole of atoms or ion in the gas phase.Step 4 in diagram on the last slide.Cl(g) + e-(g) ---> Cl-(g)ΔHEa = -349 kj/mole
15 Interactions Involving Polar Molecules An ion-dipole interaction occurs between an ion and the partial charge of a molecule with a permanent dipole.The cluster of water molecules that surround an ion in aqueous medium is a sphere of hydration.
17 The Solution Process Bond Breaking Processes Break solute particle forces (expanding the solute), endothermicBreak solvent particle forces (expanding the solvent), endothermic
18 The Solution Process Attractive Forces Energy released when solute solvent are attracted, exothermicEnergy is released due to new attractionsIon dipole if the solute is ionic and the solvent polar.London-Dipole for nonpolar solute and polar solventDipole-dipole for polar solute and polar solvent
19 The Solution Process Theromodynamics Enthalpy Entropy (Perfect crystal, assumed to be zero)Gibbs free energy
20 The Solution Process Oil dissolving in water London forces holding the oil molecules together are large do to the large surface area of the oilThe hydrogen bonds holding water molecules together are largeThe forces of attraction of between nonpolar oil and polar water are weak at bestThus the overall process is highly endothermic and not allowed thermo chemically
21 The Solution Process Oil dissolving in water Entropy should be greater than zeroFree energy should be greater than zero, since the process is highly endothermicThus the overall process is nonspontaneous
22 The Solution Process Sodium chloride dissolving in water Large amount of energy is required to break the ionic lattice of the sodium chloride (expand solute)Large amount of energy is required to separate the water molecules to expand the solvent breaking hydrogen bondsFormation of the ion dipole forces releases a large amount of energy, strong forces (why?)The sum of the enthalpies is about +6 kJ (slightly endothermic), which is easily overcome by the entropy of the solution formation.
23 Water as a SolventWater most important solvent, important to understand its solvent propertiesMost of the unusual solvent properties of water stem from it hydrogen bonding natureConsider the following ∆S of solutionKCl →75j/K-moleLiF→-36j/K-moleCaS→-138 j/K-mole
24 Water as a Solvent We would expect ∆S>0 for all solutions, right? But two are negative, why?Obviously, something must be happening for the increased order.Ion-dipole forces are ordering the water molecules around the ions, thus causing more order in water i.e. less positions for water than in the pure liquid state
25 Water as a SolventSmaller ions, have stronger ion dipole forces, thus pulling water closer, therefore less positionsAlso, ions with a charge greater than one will attract to water stronger than a one plus charge, thus more order due to less space between particles
26 Dipole-Dipole Interactions Dipole-dipole interactions are attractive forces between polar molecules.An example is the interaction between water molecules.The hydrogen bond is a special class of dipole-dipole interactions due to its strength.
27 Dipole-Dipole Forces H Cl H Cl H Cl Dipole-dipole (Polar molecules) δ+ Alignment of polar molecules to two electrodescharged + and δ–Forces compared to ionic/covalent are about 1 in strength compared to a scale of 100, thus 1%δ+δ–δ+δ–δ–δ+H Cl H Cl H Cl
29 Hydrogen BondingHydrogen bonding a stronger intermolecular force involving hydrogen and usually N, O, F, and sometimes ClStronger that dipole-dipole, about 10 out of 100, or 10Hydrogen needs to be directly bonded to the heteroatomSince hydrogen is small it can get close to the heteroatomAlso, the second factor is the great polarity of the bond.
31 Hydrogen Bonding in Water Chemistry 140 Fall 2002Hydrogen Bonding in WaterSolid ice has lower density than liquid water. H-bonding holds the ice in a rigid but open structure.Maximum density of water at 3.98 C.around a molecule in the solid in the liquid
33 Interacting Nonpolar Molecules Dispersion forces (London forces) are intermolecular forces caused by the presence of temporary dipoles in molecules.A temporary dipole (or induced dipole) is a separation of charge produced in an atom or molecule by a momentary uneven distribution of electrons.
35 Strength of Dispersion Forces The strength of dispersion forces depends on the polarizability of the atoms or molecules involved.Poarizability is a term that describes the relative ease with which an electron cloud is distorted by an external charge.Larger atoms or molecules are generally more polarizable than small atoms or molecules.
36 London Forces (Dispersion) Induced dipoles (Instantaneous )Strength is surface area dependentMore significant in larger moleculesAll molecules show dispersion forcesLarger molecules are more polarizable
38 Molar Mass and Boiling Points of Common Species. HalogenM(g/mol)Bp(K)Noble GasHe24F23885Ne2027Cl271239Ar4087Br2160332Kr84120I2254457Xe131165Rn211
39 Hydrocarbon Alcohol Molecular Formula Molar Mass Bp (oC) CH4 16.04 -161.5CH3CH330.07-88CH3OH32.0464.5CH3CH2CH344.09-42CH3CH2OH46.0778.5CH3CH(CH)CH358.12-11.7CH3CH(OH)CH360.0982CH3CH2CH2CH3-0.5CH3CH2CH2OH97
41 PracticeRank the following compound in order of increasing boiling point. CH3OH, CH3CH2CH2CH3, and CH3CH2OCH3
42 PracticeRank the following compound in order of increasing boiling point. CH3OH, CH3CH2CH2CH3, and CH3CH2OCH3MMIM ForcesCH3OH32.0London and H-bondingCH3CH2CH2CH358.0London, onlyCH3CH2OCH360.0London and Dipole-dipole
43 PracticeRank the following compound in order of increasing boiling point. CH3OH, CH3CH2CH2CH3, and CH3CH2OCH3MMIM ForcesCH3OH32.0London and H-bondingCH3CH2CH2CH358.0London, onlyCH3CH2OCH358.0London and Dipole-dipoleThe order is:CH3CH2CH2CH3 <CH3CH2OCH3<CH3OH
44 Polarity and Solubility If two or more liquids are miscible, they form a homogeneous solution when mixed in any proportion.Ionic materials are more soluble in polar solvents then in nonpolar solvents.Nonpolar materials are soluble in nonpolar solvents.Like dissolves like
45 Solubility of Gases in Water Henry’s Law states that the solubility of a sparingly soluble chemically unreactive gas in a liquid is proportional to the partial pressure of the gas.Cgas = kHPgas where C is the concentration of the gas, kH is Henry’s Law constant for the gas.
46 Henry’s Law Constants for Gas kH[mol/(L•atm)]kH[mol/(kg•mmHg)]He3.5 x 10-45.1 x 10-7O21.3 x 10-31.9 x 10-6N26.7 x 10-49.7 x 10-7CO23.5 x 10-25.1 x 10-5
47 TermsA hydrophobic (“water-fearing) interaction repels water and diminishes water solubility. Polar vs. nonpolarA hydrophilic (“water-loving”) interaction attracts water and promotes water solubility. Polar vs. polar, best with hydrogen bonding involved.
48 Types of Forces Cohesive Forces Intermolecular forces between the same particles.Adhesive ForcesIntermolecular forces between the different particles.
49 Cohesive Forces Example Beading or wetting on a surface Surface tension (resistance to increasing the surface area)Def: To increase surface area molecules must move from the middle. This requires energy j/m2The stronger the IMF the stronger the surface tensionNeedle or paper clip on top of waterBeading or wetting on a surfaceRounded surface of liquid mercury in a tube
50 Adhesive Forces Examples. Capillary rise water forms a meniscus since the forces between the glass and water are stronger than between water and water. Both are hydrogen bonds
51 Cohesive and Adhesive Forces The right tube shows cohesive forces, since mercury is nonpolar and attracts more strongly to itself, rather than to the glass (SiO2)The left test tube shows adhesive forces due to the attraction of water solvent to the polar glass (SiO2) Hydrogen bonding, right?51
52 TermsCapillary rise is the rise of a liquid up a narrow tube as a result of adhesive forces between the liquid and the tube and cohesive forces within the liquid.Viscosity is a measure of the resistance to flow of a fluid.52
54 The Liquid State Example Blood up a capillary Meniscus Adhesive ForcesIntermolecular forces between unlike moleculesExampleCapillary riseBlood up a capillaryMeniscusCapillary rise is when the adhesive forces are stronger than the cohesive forcesCapillary rise when polar bonds are present in the container walls like glass, SiO2Mercury is an example where the cohesive forces are stronger than the adhesive forces
56 The Liquid State Viscosity (resistance to flow) How fast liquids flow Due in part to intermolecular forces, but also entanglementNewton’s/m2 called poise
57 Change of State (Water) depositionfreezingCondensationH2O(s) H2O(l) H2O(g)Water Thermodynamic Properties∆Hfus = 6.02 kj/mole∆Hvap= 40.7 kj/molemeltingevaporationsublimation
58 Change of State (Water) Heat capacity of water = j/g-°CWater has a very large heat capacity since it hydrogen bonds and a lot of energy is required to break these bondsWhy water is used in radiatorsUsed to cool animals
60 Some Properties of Solids Melting PointFreezing PointSuper coolingΔHfus(H2O) = kJ/molSlide 60 of 35
61 Super Cooling and Heating Super cooled, when a liquid exists below its freezing point.Super cooling occurs when the rate of cooling is faster than it takes for the molecules to rotate for correct alignment to form crystals.When the crystals rotate and form inter-particle forces, heat is released, thus raising the temperature up to the correct m.p.Super heatedCalled bumpingUse boiling stones, cannot reuse the stonesHot vapor at bottom expands rapidly and bursts
62 Vapor PressureVaporization or evaporation is the transformation of molecules in the liquid phase to the gas phase.Vapor pressure is the force exerted at a given temperature by a vapor in equilibrium with its liquid phase.
63 Vapor PressureWhat evaporates faster pure distilled water in the beaker on the left, or seawater in the beaker on the right?? Both beakers are the same size and at the same temperature.
65 Vapor PressureYes, pure distilled water evaporates faster, since there are more water molecules on the surface to evaporate?
66 Vapor PressurePhysical properties that depend on the number of particles, and not on the particle nature are called colligative properties
67 An Aqueous Solution and Pure Water in a Closed Environment
68 Vapor Pressure Clausius-Clapeyron Equation Linear Which one is water? (e) (d) (c) (b) (a)Clausius-Clapeyron Equation( )1T-ΔHvapLinearLn P =+ BR∆SWhich one is water?(Entropy of vaporization)No Units!B = y-intercept =RSlide 68
69 ln((P1/P2) = - ΔH/R(T2-T1)/T1T2 Vapor PressureClasius Clapeyron EquationAssume data for two different temperatures and pressures to generate two separate equationsBy subtracting the equations the y-intercept component is eliminated.ln P1 = - ΔH/R(1/T1 ) + C- (ln P2 = - ΔH/R(1/T2) + C)ln((P1/P2) = - ΔH/R(1/T2 – 1/T1)Another useful version of the two point equationln((P1/P2) = - ΔH/R(T2-T1)/T1T2
70 Vapor PressureAs a liquid evaporates in a closed container the concentration of vapor increases, thus the rate of condensation increasesAs the rate of condensation is increasing eventually it will equal the constant rate of evaporation, then we have vapor in equilibrium with the liquidThe pressure of the vapor at equilibrium is called the equilibrium vapor pressure
71 Raoult’s Law Psolution = Xsolvent (Psolvent) P - vapor pressure X - mole fractionXsolvent + Xsolute = 1
72 For a Solution that Obeys Raoult's Law, a Plot fo Psoln Versus Xsolvent, Give a Straight Line
74 Liquid-Vapor Equilibrium Chemistry 140 Fall 2002Liquid-Vapor EquilibriumThe vapor phase is richer in the more volatile component.July 2009General Chemistry: Chapter 11Slide 74 of 4674
75 Two Volatile Liquids Ideal Solution Positive deviation Negative deviationPositive deviation exists when experimental value is larger than calculated value, weaker solute solvent attraction; more evaporation.Negative deviation exists when experimental value is smaller than calculated value; stronger solvent solute attraction; less evaporation
76 Fractional Distillation July 2009General Chemistry: Chapter 11Slide 76 of 46
77 Fractional Distillation July 2009General Chemistry: Chapter 11Slide 77 of 46
78 PracticeA solution contains mL of water and mol of ethanol. What is the mole fraction of water and the vapor pressure of the solution at 25oC, if the vapor of pressure of pure water is 23.8 torr?
79 PracticeA solution contains mL of water and mol of ethanol. What is the mole fraction of water and the vapor pressure of the solution at 25oC, if the vapor of pressure of pure water is 23.8 torr?100.0mL
80 PracticeA solution contains mL of water and mol of ethanol. What is the mole fraction of water and the vapor pressure of the solution at 25oC, if the vapor of pressure of pure water is 23.8 torr?1.00 gmole100.0mLmL18.0 g
81 PracticeA solution contains mL of water and mol of ethanol. What is the mole fraction of water and the vapor pressure of the solution at 25oC, if the vapor of pressure of pure water is 23.8 torr?1.00 gmole100.0mL= 5.56 molemL18.0 g0.500 mole C2H6O6.06 mole5.56XHOH == 0.9176.06
82 PracticeA solution contains mL of water and mol of ethanol. What is the mole fraction of water and the vapor pressure of the solution at 25oC, if the vapor of pressure of pure water is 23.8 torr?1.00 gmole100.0mL= 5.56 molemL18.0 g0.500 mole C2H6O6.06 molePHOH = 0.917(23.8 torr)PHOH = 21.8 torr5.56XHOH == 0.9176.06
87 Phase Diagram TermsThe triple point defines the temperature and pressure where all three phases of a substance coexist.The critical point is that specific temperature and pressure at which the liquid and gas phases of a substance have the same density and are indistinguishable for each other.A supercritical fluid is a substance at conditions above its critical temperature and pressure.
89 Colligative Properties of Solutions Colligative properties of solutions depend on the concentration and not the identity of particles dissolved in the solvent.Sea water boils at a higher temperature than pure water.
90 Calculating Changes in Boiling Point Tb = KbmTb is the increase in BpKb is the boiling-point elevation constantm is a new concentration unit called molalitymoles soluteMolality (m) =Kg solvent
91 PracticeCalculate the molality of a solution containing mol of glucose (C6H12O6) in 1.5 kg of water.
92 PracticeCalculate the molality of a solution containing mol of glucose (C6H12O6) in 1.5 kg of water.0.875 mole1.5 kg
93 PracticeCalculate the molality of a solution containing mol of glucose (C6H12O6) in 1.5 kg of water.0.875 mole= 0.58 m1.5 kg
94 PracticeSeawater contains M Cl- at the surface at 25oC. If the density of sea water is g/mL, what is the molality of Cl- in sea water?
95 PracticeSeawater contains M Cl- at the surface at 25oC. If the density of sea water is g/mL, what is the molality of Cl- in sea water?103 mL solution1.022 g= 1022 g solutionmL
96 PracticeSeawater contains M Cl- at the surface at 25oC. If the density of sea water is g/mL, what is the molality of Cl- in sea water?103 mL solution1.022 g= 1022 g solutionmL0.558 mole Cl-45.45 g Cl-= g Cl-mole Cl-
97 PracticeSeawater contains M Cl- at the surface at 25oC. If the density of sea water is g/mL, what is the molality of Cl- in sea water?103 mL solution1.022 g= 1022 g solutionmL0.558 mole Cl-45.45 g Cl-= g Cl-mole Cl-1022 g solution – g Cl- = g H2O
98 PracticeSeawater contains M Cl- at the surface at 25oC. If the density of sea water is g/mL, what is the molality of Cl- in sea water?103 mL solution1.022 g= 1022 g solutionmL0.558 mole Cl-45.45 g Cl-= g Cl-mole Cl-1022 g solution – g Cl- = g H2O0.558 mole Cl-103 g= m996.6 g H2OKg
99 PracticeCinnamon owes its flavor and odor to cinnamaldehyde (C9H8O). Determine the boiling-point elevation of a solution of 100 mg of cinnamaldehyde dissolved in 1.00 g of carbon tetrachloride (Kb = 2.34oC/m).
100 PracticeCinnamon owes its flavor and odor to cinnamaldehyde (C9H8O). Determine the boiling-point elevation of a solution of 100 mg of cinnamaldehyde dissolved in 1.00 g of carbon tetrachloride (Kb = 2.34oC/m).100 mg C9H8O10-3 mole103 gmmole= m1.00 g CCl4mgmmoleKg2.34 °Cm= 1.77°Cm
101 Freezing-point Depression Tf = KfmKf is the freezing-point depression constant and m is the molality.
102 PracticeThe freezing point of a solution prepared by dissolving X 102 mg of caffeine in 10.0 g of camphor is 3.07 Celsius degree lower than that of pure camphor (Kf = 39.7oC/m). What is the molar mass of caffeine?
103 The van’t Hoff Factor Tb = iKbm & Tf = iKfm van’t Hoff factor, i is the number of ions in one formula unit
104 The van’t Hoff Factor Used for ionic compounds, why not osmolarity? The value of i assumes that all of the salt dissolves and dissociates in to its component ionsThis is not always true, for example 0.10m NaCl I is 1.87Ion pairing often occurs in solutionsIon pairing most important in concentrated solutionsIon pairing important in highly charged solutions
106 PracticeCaCl2 is widely used to melt frozen precipitation on sidewalks after a winter storm. Could CaCl2 melt ice at -20oC? Assume that the solubility of CaCl2 at this temperature is 70.0 g/100.0 g of H2O and that the van’t Hoff factor for a saturated solution of CaCl2 is 2.5 (Kf for water is C/m).
107 Osmotic PressureOsmotic pressure () is the pressure that has to be applied across a semipermeable membrane to stop the flow of solvent form the the compartment containing pure solvent or a less concentrated solution towards a more concentrated solution. = iMRT where i is the van’t Hoff factor, M is molarity of solute, R is the idea gas constant ( l•atm/(mol•K)), and T is in Kelvin107
109 Osmotic pressure Equation from the ideal gas law (pv = nRT) = MRT Semi permeable membraneIsotonic same concentrationCells placed in lower concentration hypotonic, cell will swell called hemolosisIf concentration on the outside of the cells is greater then the solution is called hypertonic and the cells shrink called crenation
110 Osmosis In osmosis, solvent passes through a semipermeable membrane to balance the concentration of solutes in solution on both sidesof the membrane.Figure 10.30
111 ChemTour: Lattice Energy Click to launch animationPC | MacStudents learn to apply Coulomb’s law to calculate the exact lattice energies of ionic solids. Includes Practice Exercises.
112 ChemTour: Intermolecular Forces Click to launch animationPC | MacThis ChemTour explores the different types of intermolecular forces and explains how these affect the boiling point, melting point, solubility, and miscibility of a substance. Includes Practice Exercises.
113 Click to launch animation ChemTour: Henry’s LawClick to launch animationPC | MacStudents learn to apply Henry’s law and calculate the concentration of a gas in solution under varying conditions of temperature and pressure. Includes interactive practice exercises.
114 ChemTour: Molecular Motion Click to launch animationPC | MacStudents use an interactive graph to explore the relationship between kinetic energy and temperature. Includes Practice Exercises.
115 ChemTour: Raoult’s Law Click to launch animationPC | MacStudents explore the connection between the vapor pressure of a solution and its concentration as a gas above the solution. Includes Practice Exercises.
116 ChemTour: Phase Diagrams Click to launch animationPC | MacStudents use an interactive phase diagram and animated heating curve to explore how changes in temperature and pressure affect the physical state of a substance.
117 ChemTour: Capillary Action Click to launch animationPC | MacIn this ChemTour, students learn that certain liquids will be drawn up a surface if the adhesive forces between the liquid on the surface of the tube exceed the cohesive forces between the liquid molecules.
118 ChemTour: Boiling and Freezing Click to launch animationPC | MacStudents learn about colligative properties by exploring the relationship between solute concentration and the temperature at which a solution will undergo phase changes. Interactive exercises invite students to practice calculating the boiling and freezing points of different solutions.
119 ChemTour: Osmotic Pressure Click to launch animationPC | MacStudents discover how a solute can build up pressure behind a semipermeable membrane. This tutorial also discusses the osmotic pressure equation and the van’t Hoff factor.
121 Solubility of CH4, CH2Cl2, and CCl4 Consider the following arguments for each answer and vote again:A gas is inherently easier to dissolve in a liquid than is another liquid, since its density is much lower.The polar molecule CH2Cl2 can form stabilizing dipole-dipole interactions with the water molecules, corresponding to a decrease in ΔH°soln.The nonpolar molecule CCl4 has the largest molecular mass, and so is most likely to partially disperse into the water, corresponding to an increase in ΔS°soln.Answer: BSolubility of CH4, CH2Cl2, and CCl4