Have studied INTRAmolecular forces the forces holding atoms

Ion-Ion Forces for comparison of magnitude Na+—Cl- in salt These are the strongest forces.

Covalent Bonding Forces for comparison of magnitude C=C, 610 k. J/mol C–C, 346 k.

Attraction Between Ions and Permanent Dipoles Water is highly polar and can interact with

Attraction Between Ions and Permanent Dipoles Many metal ions are hydrated. This is the

Attraction Between Ions and Permanent Dipoles Attraction between ions and dipole depends on ion

Dipole-Dipole Forces Such forces bind molecules having permanent dipoles to one another. © 2006

Dipole-Dipole Forces Influence of dipole-dipole forces is seen in the boiling points of simple

Hydrogen Bonding A special form of dipole-dipole attraction, which enhances dipole-dipole attractions. H-bonding is

Hydrogen Bonding in H 2 O H-bonding is especially strong in water because •

Hydrogen Bonding in H 2 O Ice has open lattice -like structure. Ice density

Hydrogen Bonding in H 2 O Ice has open lattice-like structure. Ice density is

Hydrogen Bonding in H 2 O H bonds ---> abnormally high specific heat capacity

Hydrogen Bonding H bonds leads to abnormally high boiling point of water. © 2006

Boiling Points of Simple Hydrogen-Containing Compounds Active Figure 13. 8 © 2006 Brooks/Cole -

Hydrogen Bonding in Biology H-bonding is especially strong in biological systems — such as

Double helix of DNA Portion of a DNA chain © 2006 Brooks/Cole - Thomson

Base-Pairing through H-Bonds © 2006 Brooks/Cole - Thomson

FORCES INVOLVING INDUCED DIPOLES How can non-polar molecules such as O 2 and I

FORCES INVOLVING INDUCED DIPOLES Solubility increases with mass the gas © 2006 Brooks/Cole -

FORCES INVOLVING INDUCED DIPOLES • Process of inducing a dipole is polarization • Degree

IM FORCES — INDUCED DIPOLES Consider I 2 dissolving in ethanol, CH 3 CH

FORCES INVOLVING INDUCED DIPOLES Formation of a dipole in two nonpolar I 2 molecules.

FORCES INVOLVING INDUCED DIPOLES The magnitude of the induced dipole depends on the tendency

Boiling Points of Hydrocarbons C 4 H 10 C 3 H 8 C 2

Intermolecular Forces Summary © 2006 Brooks/Cole - Thomson

Measuring Equilibrium Vapor Pressure Liquid in flask evaporates and exerts pressure on manometer. Active

Equilibrium Vapor Pressure Active Figure 13. 18 © 2006 Brooks/Cole - Thomson

Liquids Equilibrium Vapor Pressure FIGURE 13. 18: VP as a function of T. 1.

Liquids HEAT OF VAPORIZATION is the heat req’d (at constant P) to vaporize the

Phase Diagrams © 2006 Brooks/Cole - Thomson

TRANSITIONS BETWEEN PHASES Section 13. 10 Lines connect all conditions of T and P

Phase Diagram for Water Liquid phase Solid phase Gas phase © 2006 Brooks/Cole -

Phase Equilibria — Water Solid-liquid Gas-Liquid Gas-Solid © 2006 Brooks/Cole - Thomson

Triple Point — Water At the TRIPLE POINT all three phases are in equilibrium.

Phases Diagrams— Important Points for Water T(˚C) P(mm. Hg) Normal boil point 100 760

Critical T and P As P and T increase, you finally reach the CRITICAL

Critical T and P COMPD T c (o C ) Pc(atm) H 2 O

Solid-Liquid Equilibria In any system, if you increase P the DENSITY will go up.

Solid-Liquid Equilibria P Solid H 2 O Liquid H 2 O Raising the pressure

CO 2 Phase Diagram © 2006 Brooks/Cole - Thomson

CO 2 Phases Separate phases Figure 13. 41 © 2006 Brooks/Cole - Thomson Increasing

Dissolving An Ionic Solid Active Figure 14. 9 © 2006 Brooks/Cole - Thomson

Energetics of the Solution Process Figure 14. 8 © 2006 Brooks/Cole - Thomson

Energetics of the Solution Process If the enthalpy of formation of the solution is

Colligative Properties On adding a solute to a solvent, the props. of the solvent

Concentration Units MOLE FRACTION, X For a mixture of A, B, and C MOLALITY,

Calculating Concentrations Dissolve 62. 1 g (1. 00 mol) of ethylene glycol in 250.

Understanding Colligative Properties To understand colligative properties, study the LIQUIDVAPOR EQUILIBRIUM for a solution.

Understanding Colligative Properties VP of H 2 O over a solution depends on the

Raoult’s Law An ideal solution is one that obeys Raoult’s law. PA = XA

Raoult’s Law Assume the solution containing 62. 1 g of glycol in 250. g

Changes in Freezing and Boiling Points of Solvent • • For a 2 -component

Vapor Pressure Lowering Figure 14. 14 © 2006 Brooks/Cole - Thomson

The boiling point of a solution is higher than that of the pure solvent.

Elevation of Boiling Point Elevation in BP = ∆TBP = KBP • m (where

Change in Boiling Point Dissolve 62. 1 g of glycol (1. 00 mol) in

Change in Freezing Point Pure water Ethylene glycol/water solution The freezing point of a

Lowering the Freezing Point Water with and without antifreeze © 2006 Brooks/Cole - Thomson

Freezing Point Depression Calculate the FP of a 4. 00 molal glycol/water solution. KFP

Freezing Point Depression How much Na. Cl must be dissolved in 4. 00 kg

Boiling Point Elevation and Freezing Point Depression ∆T = K • m • i

Osmosis The semipermeable membrane allows only the movement of solvent molecules. Solvent molecules move

Osmosic Pressure, ∏ Osmotic pressure © 2006 Brooks/Cole - Thomson Equilibrium is reached when

Osmosis and Living Cells © 2006 Brooks/Cole - Thomson

Reverse Osmosis Water Desalination Water desalination plant in Tampa © 2006 Brooks/Cole - Thomson

Osmosis Calculating a Molar Mass Dissolve 35. 0 g of hemoglobin in enough water

Slides: 70

Download presentation

Have studied INTRAmolecular forces— the forces holding atoms together to form molecules. Now turn to forces between molecules — INTERmolecular forces. Forces between molecules, between ions, or between molecules and ions. © 2006 Brooks/Cole - Thomson Intermolecular Forces

Ion-Ion Forces for comparison of magnitude Na+—Cl- in salt These are the strongest forces. Lead to solids with high melting temperatures. Na. Cl, mp = 800 o. C Mg. O, mp = 2800 o. C © 2006 Brooks/Cole - Thomson

Attraction Between Ions and Permanent Dipoles Attraction between ions and dipole depends on ion charge and ion-dipole distance. Measured by ∆H for Mn+ + H 2 O --> [M(H 2 O)x]n+ -1922 k. J/mol © 2006 Brooks/Cole - Thomson -405 k. J/mol -263 k. J/mol

Dipole-Dipole Forces Influence of dipole-dipole forces is seen in the boiling points of simple molecules. Compd Mol. Wt. Boil Point N 2 28 -196 o. C CO 28 -192 o. C Br 2 160 59 o. C ICl 162 97 o. C © 2006 Brooks/Cole - Thomson

Hydrogen Bonding in H 2 O H-bonding is especially strong in water because • the O—H bond is very polar • there are 2 lone pairs on the O atom Accounts for many of water’s unique properties. © 2006 Brooks/Cole - Thomson

Hydrogen Bonding in H 2 O Ice has open lattice-like structure. Ice density is < liquid and so solid floats on water. One of the VERY few substances where solid is LESS DENSE than the liquid. © 2006 Brooks/Cole - Thomson

Hydrogen Bonding in H 2 O H bonds ---> abnormally high specific heat capacity of water (4. 184 J/g • K) This is the reason water is used to put out fires, it is the reason lakes/oceans control climate, and is the reason thunderstorms release huge energy. © 2006 Brooks/Cole - Thomson

Hydrogen Bonding in Biology H-bonding is especially strong in biological systems — such as DNA — helical chains of phosphate groups and sugar molecules. Chains are helical because of tetrahedral geometry of P, C, and O. Chains bind to one another by specific hydrogen bonding between pairs of Lewis bases. —adenine with thymine —guanine with cytosine © 2006 Brooks/Cole - Thomson

FORCES INVOLVING INDUCED DIPOLES How can non-polar molecules such as O 2 and I 2 dissolve in water? The water dipole INDUCES a dipole in the O 2 electric cloud. Dipole-induced dipole © 2006 Brooks/Cole - Thomson

FORCES INVOLVING INDUCED DIPOLES • Process of inducing a dipole is polarization • Degree to which electron cloud of an atom or molecule can be distorted in its polarizability. © 2006 Brooks/Cole - Thomson

IM FORCES — INDUCED DIPOLES Consider I 2 dissolving in ethanol, CH 3 CH 2 OH. -d I-I -d O R H +d © 2006 Brooks/Cole - Thomson I-I The alcohol temporarily creates or INDUCES a dipole in I 2. +d -d O R H +d

FORCES INVOLVING INDUCED DIPOLES Formation of a dipole in two nonpolar I 2 molecules. Induced dipole-induced dipole The induced forces between I 2 molecules are very weak, so solid I 2 sublimes (goes from a solid to gaseous molecules). © 2006 Brooks/Cole - Thomson

FORCES INVOLVING INDUCED DIPOLES The magnitude of the induced dipole depends on the tendency to be distorted. Higher molec. weight ---> larger induced dipoles. Molecule Boiling Point (o. C) CH 4 (methane) - 161. 5 C 2 H 6 (ethane) - 88. 6 C 3 H 8 (propane) - 42. 1 C 4 H 10 (butane) - 0. 5 © 2006 Brooks/Cole - Thomson

Liquids Equilibrium Vapor Pressure FIGURE 13. 18: VP as a function of T. 1. The curves show all conditions of P and T where LIQ and VAP are in EQUILIBRIUM 2. The VP rises with T. 3. When VP = external P, the liquid boils. This means that BP’s of liquids change with altitude. 4. If external P = 760 mm Hg, T of boiling is the NORMAL BOILING POINT 5. VP of a given molecule at a given T depends on IM forces. Here the VP’s are in the order ether O C 2 H 5 H 5 C 2 dipole alcohol O H 5 C 2 H H-bonds increasing strength of IM interactions © 2006 Brooks/Cole - Thomson water O H H extensive H-bonds

Liquids HEAT OF VAPORIZATION is the heat req’d (at constant P) to vaporize the liquid. LIQ + heat ---> VAP Compd. ∆Hvap (k. J/mol) H 2 O 40. 7 (100 o. C) H-bonds SO 2 26. 8 (-47 o. C) dipole Xe 12. 6 (-107 o. C) induced dipole © 2006 Brooks/Cole - Thomson IM Force

TRANSITIONS BETWEEN PHASES Section 13. 10 Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side of the line. (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example. ) © 2006 Brooks/Cole - Thomson

Critical T and P As P and T increase, you finally reach the CRITICAL T and P Above critical T no liquid exists no matter how high the pressure. At P < 4. 58 mm. Hg and T < 0. 0098 ˚C solid H 2 O can go directly to vapor. This process is called SUBLIMATION This is how a frost-free refrigerator works. © 2006 Brooks/Cole - Thomson

Solid-Liquid Equilibria In any system, if you increase P the DENSITY will go up. Therefore — as P goes up, equilibrium favors phase with the larger density (or SMALLER volume/gram). Liquid H 2 O Solid H 2 O Density cm 3/gram © 2006 Brooks/Cole - Thomson 1 g/cm 3 1 0. 917 g/cm 3 1. 09

Solid-Liquid Equilibria P Solid H 2 O Liquid H 2 O Raising the pressure at constant T causes water to melt. Normal freezing point 760 mm. Hg 0 °C The NEGATIVE SLOPE of the S/L line is unique to H 2 O. Almost everything else has positive slope. T The behavior of water under pressure is an example of LE CHATELIER’S PRINCIPLE At Solid/Liquid equilibrium, raising P squeezes the solid. It responds by going to phase with greater density, i. e. , the liquid phase. © 2006 Brooks/Cole - Thomson

Energetics of the Solution Process If the enthalpy of formation of the solution is more negative that of the solvent and solute, the enthalpy of solution is negative. The solution process is exothermic! © 2006 Brooks/Cole - Thomson

Colligative Properties On adding a solute to a solvent, the props. of the solvent are modified. • Vapor pressure decreases • Melting point decreases • Boiling point increases • Osmosis is possible (osmotic pressure) These changes are called COLLIGATIVE PROPERTIES. They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles. © 2006 Brooks/Cole - Thomson

Understanding Colligative Properties VP of H 2 O over a solution depends on the number of H 2 O molecules per solute molecule. Psolvent proportional to Xsolvent Psolvent = Xsolvent • Posolvent VP of solvent over solution = (Mol frac solvent) • (VP pure solvent) RAOULT’S LAW © 2006 Brooks/Cole - Thomson

Raoult’s Law An ideal solution is one that obeys Raoult’s law. PA = XA • Po. A Because mole fraction of solvent, XA, is always less than 1, then PA is always less than Po. A. The vapor pressure of solvent over a solution is always LOWERED! © 2006 Brooks/Cole - Thomson

Raoult’s Law Assume the solution containing 62. 1 g of glycol in 250. g of water is ideal. What is the vapor pressure of water over the solution at 30 o. C? (The VP of pure H 2 O is 31. 8 mm Hg; see App. E. ) © 2006 Brooks/Cole - Thomson

Changes in Freezing and Boiling Points of Solvent • • For a 2 -component system where A is the solvent and B is the solute ∆PA = VP lowering = XBPo. A VP lowering is proportional to mol frac solute! For very dilute solutions, ∆PA = K • molality. B where K is a proportionality constant. • This helps explain changes in melting and boiling points. © 2006 Brooks/Cole - Thomson

Boiling Point Elevation and Freezing Point Depression ∆T = K • m • i A generally useful equation i = van’t Hoff factor = number of particles produced per formula unit. Compound Theoretical Value of i glycol 1 Na. Cl 2 Ca. Cl 2 3 © 2006 Brooks/Cole - Thomson

Osmosis The semipermeable membrane allows only the movement of solvent molecules. Solvent molecules move from pure solvent to solution in an attempt to make both have the same concentration of solute. Driving force is entropy © 2006 Brooks/Cole - Thomson

Osmosic Pressure, ∏ Osmotic pressure © 2006 Brooks/Cole - Thomson Equilibrium is reached when pressure — the OSMOTIC PRESSURE, ∏ — produced by extra solution counterbalances pressure of solvent molecules moving thru the membrane. ∏ = c. RT (c is conc. in mol/L)

Osmosis Calculating a Molar Mass Dissolve 35. 0 g of hemoglobin in enough water to make 1. 00 L of solution. ∏ measured to be 10. 0 mm Hg at 25 ˚C. Calculate molar mass of hemoglobin. © 2006 Brooks/Cole - Thomson