Principles of Chemistry II © Vanden BoutJust to be clear about Free EnergyG = H - TSGTstraight line assumes that H and S are independent of temperatureSlope is given by SLiquid has a larger entropyand therefore a steeper slopeLiquidSolidTmT > TmLiquid hasthe lower freeenergyT < TmSolid hasthe lower freeenergy Principles of Chemistry II © Vanden BoutKinetically trapped in non-equilibrium state"Super-cooled" trapped in liquid state due to slow crystal formation"Super-heated" trapped in liquid state due to slow bubble formationSuper Cooled or Super HeatedDemo Principles of Chemistry II © Vanden BoutLast Phase change! A.!! liquids only boil at 1 atm total pressure ! B.!! liquids only evaporate at room temperature! C.!! bubble form in liquids when boiling! D.!! nothing!What is a key difference between evaporation and boiling? Principles of Chemistry II © Vanden BoutSolutionsSolutions are homogeneous mixtures of multiple compoundsSolutionsalt waterairsteelMajor component = Solvent (language typically used for liquids)Minor component = SolutePrinciples of Chemistry II © Vanden BoutLet's look at the following "reaction"water + salt ------> "salt water"Which has the higher entropy?! A.!! The water + the solid salt ! B.!! The solution! C.!! They are exactly the same! Principles of Chemistry II © Vanden BoutLet's look at the following "reaction"water + salt ------> "salt water"Which has the lower free energy?! A.!! The water + the solid salt ! B.!! The solution! C.!! They are exactly the same! Principles of Chemistry II © Vanden BoutLet's look at the following "reaction"water + salt ------> "salt water"Which has the higher enthalpy?! A.!! The water + the solid salt ! B.!! The solution! C.!! They are essentially the same! Principles of Chemistry II © Vanden BoutWhat is enthalpy change for making a solution?What has to happen?Lose solvent-solvent interactions (IMF)Lose solute-solute interactions (IMF)Gain solute-solvent interactionsFigure Copyright Houghton Mifflin Company. All rights reservedPrinciples of Chemistry II © Vanden BoutEnthalpy of Solvation !Hsolvationhard to predict!Hsolvation = 0Ideal solutionSolute-solvent interactions are identical to solute-solute and solvent-solvent!Hsolvation > 0TypicalSolute-solvent interactions are weaker thansolute-solute and solvent-solvent!Hsolvation < 0Unusual but possibleSolute-solvent interactions are stronger thansolute-solute and solvent-solvent Principles of Chemistry II © Vanden BoutSolutions have a higher entropy than the unmixed compoundsTherefore !Ssolvation > 0Entropy of Solvation !Ssolvationeasy to predict Principles of Chemistry II © Vanden Bout Principles of Chemistry II © Vanden BoutIf !Gsolvation < 0 solution strongly favoredIf !Gsolvation > 0 undissolved state is strongly favored!Gsolvation = !Hsolvation - T !Ssolvation Best case !Hsolvation < 0 Generally the best you can hope for is !Hsolvation = 0 idealGibb's Free Energy of Solvation !GsolvationPrinciples of Chemistry II © Vanden BoutWhat makes an ideal solution?Same IMF for solute-solvent and solute-solute and solvent-solvent"like dissolves like"Polar compounds dissolve polar compounds (ionic)Nonpolar compound dissolve nonpolar compounds Principles of Chemistry II © Vanden BoutWhich is most likely to dissolve best in water?! A.!! methanol CH3OH ! B.!! butanol C4H9OH! C.!! octanol C8H17OH! D.!! didodecanol C12H25OH! Principles of Chemistry II © Vanden BoutWhich is most likely to dissolve best in hexane (C6H14)?! A.!! methanol CH3OH ! B.!! butanol C4H9OH! C.!! octanol C8H17OH! D.!! didodecanol C12H25OH! Principles of Chemistry II © Vanden BoutTemperature DependenceGenerally at T goes up solubility increasesPrinciples of Chemistry II © Vanden BoutGas Dissolved in a LiquidHenry's LawPsolute = KsolventXsolutemole fraction Principles of Chemistry II © Vanden BoutIn GeneralHenry's Law constants increase with increasing TemperatureLess gas is dissolved at higher temperatures Principles of Chemistry II © Vanden BoutPhase Diagram of CO2Figure Copyright Houghton Mifflin Company. All rights reserved Principles of Chemistry II © Vanden BoutPhase Diagram of WaterFigure Copyright Houghton Mifflin Company. All rights reservedAt a constant temperature, increasing the pressure will cause ice to melt (it moves to the higher density phase which for water is a liquid)Principles of Chemistry II © Vanden BoutPhase Diagram of WaterMany different solid phases. At very high pressure the liquid will solidifyhttp://www.lsbu.ac.uk/water/images/phase.gif Principles of Chemistry II © Vanden BoutOther SubstancesFigure Copyright Houghton Mifflin Company. All rights
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