∆H1

Solute

∆H2

solvent

∆H3

Solute-solvent

∆Hsolution

overall

outcome

Polar solute (EtOH)

Polar solvent (water)

Large + Large + Large - Small (- or +) Soln forms

(if ∆Hsolution

not too positive)

∆G =∆H + T∆S ∆G = + for spontaneous processes

∆H1Solute pull apart solute particles

∆H2 Solvent – pull apart solvent molecules

∆H3 attraction of solute and solvent

not too positive)

Nonpolar solute (oil)

Polar solvent (water)

Small + Large + Small - Large + No solution

Non-polar solute (oil)

Non-polar solvent (gasoline)

Small + Small + Small - Small (+ or -) Solution forms

(~ideal)

Polar solute (EtOH)

Non-polar solvent (oil)

Large + Small + Small - Large + No solution

forms

Ionic solute (NaCl)

Polar solvent (water)

Large + Large + Large - Small (+ or -)

(can be

relatively large)

Solution forms if

∆Hsolution not too

positive

if ∆Hsolution + solution process is “entropy driven”

Like dissolves like

� # 21 Which likely to be soluble in benzene

� CCl4 or NaCl

� Hexane or glycerol

� Acetic acid or hexanoic acid

� HCl or propyl chloride� HCl or propyl chloride

Temp effect – gases

� Gas + liquid � solution + energy

� Temp increase increases energy available

� Favors “dis” solution

� Thermal pollution – effect on fish� Thermal pollution – effect on fish

# 25 and 26

� PbCl2 NaOH

� ∆H for dissociation to aqueous ions

� Using data from Ch 8 or appendix

� Will solubility increase with increasing temp?

Pressure effect on solubility

� Henry’s law

� Increased pressure increase gas solubility

� Cg = k Pg

� Pg = partial pressure of the gas above liquid

� k – constant – characteristic of particular gas/liquid system� k – constant – characteristic of particular gas/liquid system

� Carbonated beverages

� The bends –� Difference in solubility of gases (nitrogen or helium as carrier gas) with

increasing P

� Decompressing after diving

� Hyperbaric chambers for CO poisoning, wound healing etc (direct solubility)

� Practice # 29

Typical Henry’s law problem

� He in water 3.8 X 10-4 M/atm @ 25 oC (k)

� ? M/mm Hg

� pHe =293 mm Hg @ 25 oC, what is [ ] in M

� Cg = k Pg Cg = k Pg

� HW: 27, 29 Ch 10

Colligative properties

� Due to number of particles in solution

� Be familiar with

� Electrolytes (soluble salts, SA, SB)

� Completely dissociate into ions

� Non-electrolytes

Molecular compounds (no ions)� Molecular compounds (no ions)

� Polar molecular compounds are water soluble

� Weak electrolytes

� WA, WB – partially dissociate

� Note worksheet

Colligative properties

� Due to number of particles in solution

� 1 mole sugar per liter = ? mol/L particles?

� 1 mole NaCl per liter

� 1 mole aluminum sulfate per liter� 1 mole aluminum sulfate per liter

� 1 mole acetic acid

� Electrolytes/nonelectrolytes

Vapor pressure

� Pressure of the vapor above a liquid or solution –depends on temp and identity

� Raoult’s law - mix with volatile solute

� VPsoln = XsoluteVP solute + XsolventVPsolvent

evaporation

Ideal solution of 2 volatile solvents (liquids)1. What is the VP of pure hexane ___2. What is the VP of pure pentane ___3. Which is more volatile? 4. If X = 0.5, what is VP due to pentane___ hexane ___total VP _____

Related exercise:1 mol benzene (C6H6), P

o = 75 torr 2 mol toluene (C7H8) P

o = 22 torrWhat is the mf of benzene in the mixture?What is the vp of the mixture?

Raoult’s Law VPT = XAVPA + XBVPB

What is the vp of the mixture?What is the mf of benzene in the vapor phase?

Data is for a given tempsince pentane is a liquidat RT, this must be for ahigher T

VP lowering

� Non-volatile solutes decrease vp

� Independent of nature of solute

� Dependent on number of particles in solution

� Raoult’s law -- except solute does not exert vp (non-volatile) volatile)

� VPsolution = XsolventVPsolvent

� VPlowering = XsoluteVpsolvent

� VPsolution + Vplowering = VPsolvent

� VPsolution = XsolventVPsolvent

� VPlowering = XsoluteVPsolvent

� VPsolution + VPlowering = VPsolvent

Normally used with non-electrolytes� Normally used with non-electrolytes

� # 35

Note: mole fraction concentration unit used

Boiling point elevation

� If solutes depress vp, to boil (vp = 760) temp must be elevated� Depends on concentration of particles in solution and on

solvent

� Use molality mol solute particles/kg solvent

� BP elevation = k i m� BP elevation = k i m� k= bp constant for solvent

� i= activity of solute (# particles/mol)

� m = molality of solute (mol solute/kg solvent)

� 31,32 (bp’s)

� Lab Wed benzoic acid in lauric acid

Freezing point depression

� Solutes interfere with crystal formation

� Salt added to ice – interferes with crystal structure, ice structures breaks down – endothermicprocess!!!!

� Ocean water – ice bergs are fresh water --salt is not � Ocean water – ice bergs are fresh water --salt is not included

� 1.86oC/mole of particles in 1 kg water

� Melting ice

� 31, 32

� General Chemistry Online: FAQ: Solutions: Why does salt melt ice?

Review spec lab end of class

� Assignments due

� Make sugar solns

� Spec lab:

� Calc k

� Calc energies

� Calc unk conc

� Emitted and abs colors

� Resubmit

� HW Ch 10 28-30 (Henry’s) 39 40 42-44 (fp, bp)