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Solutions and Chemical Equilibrium

Solutions and Chemical Equilibrium. Preparation for College Chemistry Columbia University Department of Chemistry. Concentration of Solutions. Colligative Properties. Osmosis and Osmotic Pressure. Chemical Equilibrium. Ion Product of Water. Chapter Outline. gas. gas. air. Gas. Liquid.

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Solutions and Chemical Equilibrium

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  1. Solutions and Chemical Equilibrium Preparation for College Chemistry Columbia University Department of Chemistry

  2. Concentration of Solutions Colligative Properties Osmosis and Osmotic Pressure Chemical Equilibrium Ion Product of Water Chapter Outline

  3. gas gas air Gas Liquid gas liquid Coke Liquid liquid liquid antifreeze Liquid solid liquid Coke Solid gas solid H2 in Pt Solid solid solid alloys Types of Solutions Phase Solute Solvent Example

  4. Mass percent % m/m (msolute/msolution )x100 Volume percent % v/v (vsolute/vsolution )x100 Mass/volume percent % m/v (msolute/vsolution )x100 Parts per million ppm mgsolute/Lsolution Parts per billion ppb µgsolute/Lsolution Molarity M molsolute/Lsolution Molality molsolute/kgsolvent m Concentration of Solutions Definition Units Symbol

  5. Mass % solute = x 100 mass solute Total mass solution mass solute total mass solution ppm solute = x 10 6 Mass % Solute When concentration is so low that the d ~ dwater: ppm solute(aqueous solutions) = mg solute / Lsolution ppb solute = mass % x 10 9 ppb solute (aqueous solutions) = µg solute / Lsolution http://pubs.acs.org:80/hotartcl/est/99/oct/oct-news5.html

  6. moles solute Liter solution mol L 1 mole AgNO3 L 169.91g 0.035 mole AgNO3 Molarity = [solute] = M = What volume of a 0.035 M AgNO3 solution can be made from 5.0 g AgNO3 ? 5.0 g AgNO3 x 840 mL x =

  7. Ci Vi Cf = Vf 250mL Cf Vf Ci Vi = Dilution Equation Only solvent is added Preparing a dilute solution of specified concentration

  8. 0 P1 Positive Negative Ideal 1 0 X1 Raoult’s Law P1 Basis for four properties of DILUTE SOLUTIONS

  9. Colligative Properties Depend on the concentration of solute species and not on its nature • Freezing point depression. Kf (°C kgsolvent mol -1solute) • Boiling point elevation Kb (°C kgsolvent mol -1solute) • Vapor-pressure lowering (atm) • Osmotic Pressure (atm)

  10. 1000 800 600 Vapor pressure (torr) 400 200 0 100 120 20 60 80 40 Temperature(°C) Vapor-pressure of liquids Pressure exerted by a vapor in equilibrium with its liquid For water: Atmospheric pressure boiling point

  11. Vapor-pressure lowering For a two component system : solvent 1, solute 2: Raoult Law: The vapor pressure lowering is The change in vapor pressure of the solvent is proportional to the mole fraction of the solute (< 0)

  12. ∆Tb P0solvent ∆P1 P0solution Boiling Point Elevation (∆Tb) Vapor Pressure lowering (∆P1) 1 atm Solvent vapor pressure Tb Temperature T’b

  13. ∆Tb and∆Tf ∆Tb =Tb’ - Tb = Kbm ∆Tf = Tf’ - Tf = -Kfm ∆Tb = b.p. elevation Kb = b.p. elevation constant ∆Tf = f.p. depression Kf = f.p. depression constant

  14. Kb Kf b.p.(°C) m.p (°C) Solvent 0.00 0.512 1.86 100.0 Water 3.07 3.90 118.5 16.6 Acetic acid 80.1 2.53 5.1 Benzene 5.5 178 208.1 40 Camphor 5.95 Kf and Kb (°C kgsolvent mol -1solute)

  15. Osmosis and Osmotic Pressure, p Jacobus van’t Hoff in 1887 c = M; R = universal gas constant; T absolute temperature Solution Pure water Semipermeable membrane

  16. T T Chemical Equilibrium N2O4 2NO2 2NO2 N2O4 N2O4 2NO2 REVERSIBLE REACTION: forward PRODUCTS REACTANTS reverse

  17. RATEforward C + D A + B RATEreverse A + B C + D Kinetics. Rates of Reaction RATEforward = RATEreverse Reaction rate Equilibrium Time

  18. NaCl (s) Na+(aq) + Cl -(aq) H3O+(aq) + C2H3O2 -(aq) HC2H3O2 (aq) Fe(SCN)2+ (aq) Fe 3+ (aq) + SCN - (aq) Chemical Equilibrium Saturated solution Weak electrolyte dissociation Complex ion formation

  19. Le’Chatelier’s Principle “A system in equilibrium that is subjected to a stress will react in ways that counteract the stress” Four ways to stress a chemical system: • Concentration Change • Volume Change • Temperature Change • Presence of a Catalyst

  20. cC + dD aA + bB cC(g) + dD(g) aA(g) + bB(g) [C] c [D] d Keq = [A] a [B] b (PD) d (PC) c Keq = (PB) b (PA) a Equilibrium Constants, Keq Kc Kp LAW OF MASS ACTION. Guldberg and Waage. 1867

  21. RATEforward [C] c [D] d Q = [C] c [A] a [D] d [B] b Q>K Keq = [A] a [B] b Q<K RATEreverse Reaction Quotient, Q Reaction quotient Q=K Time

  22. Writing Equilibrium Constants • Gases enter equilibrium expressions as partial • pressures in atm • Dissolved species enter as concentrations in M • Pure solids and pure liquids are represented by the • number 1 (unity) • A solvent in a chemical reaction is represented by 1, • provided the solution is diluted

  23. H2O + H2O H3O+(aq) + OH-(aq) [H3O +] [OH -] Keq = 1kg H2O 1 mol H2O 103 g H2O [H2O] 2 1L H2O 1kg H2O 18 g H2O x x Keq [H2O] 2 = Kw = [H3O +] [OH -] = 1x 10 -14 [H3O +] = [OH -] = 1x 10 -7 M Ion Product Constant for Water, KW Autoionization of Water [H2O] = = 55.5 M

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