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Unit 2: Liquids and solids, solubility, equilibrium

Unit 2: Liquids and solids, solubility, equilibrium. Will Barkalow and Price Ryan. Intermolecular forces. In order from weakest to strongest London Dispersion – non-polar/non-polar Dipole-Dipole – polar/polar Hydrogen Bond – ultra polar/ultra polar H with N,O,F metalli c ionic

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Unit 2: Liquids and solids, solubility, equilibrium

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  1. Unit 2: Liquids and solids, solubility, equilibrium Will Barkalow and Price Ryan

  2. Intermolecular forces • In order from weakest to strongest • London Dispersion – non-polar/non-polar • Dipole-Dipole – polar/polar • Hydrogen Bond – ultra polar/ultra polar • H with N,O,F • metallic • ionic • Covalent Bond (network) – certain C-family elements and compounds

  3. Cubic crystal structure • Simple Cubic (1 atom) • V = e3 = 8r3 • Body-Centered Cubic (2 atoms) • 4r = e • V = e3 =(4r/ )3 • Face-Centered Cubic (4 atoms) • V = e3 = (4r/ )3

  4. Phase Changes • Matter exists as solids, liquids, or gases • Matter changes between these three phases based on temperature or atmospheric pressure

  5. Phase diagram • Phase Diagrams – show which state matter exist at certain temp and pressure • Triple Point (T) – all three phases are at equilibrium • Critical Point (C) – highest temp of pressure where a distinct gas and liquid phase can exist • Supercritical Fluid (SCF) – liquid and gas phases are indistinguishable

  6. Solubility • The amount of substance that can be dissolved in a solvent at a given temperature (g/L) • Some Simple Solubility Rules • NO3- is always soluble • C2H3O2- is always soluble • OH- is insoluble with everything except alkali metals, NH4+, Ca2+, Sr2+, and Ba2+ • PO43- is insoluble with everything except alkali metals and NH4+

  7. Equilibrium • aA + bBcC + dD • Occurs when opposing reactions proceed at equal rates with constant concentrations • KC = equilibrium constant • KC = {[C]c[D]d}/{[A]a[B]b} • No Solids and Liquids included in equation • Q = Reaction Quotient • Q = {[C]c[D]d}/{[A]a[B]b} • When not at equilibrium • Q < K  Shift Right, Q > K  Shift Left, Q = K  Equilibrium Established • No solids or liquids included in equation

  8. Equilibrium continued • KP = KC(RT)-n • or same expression as Kc, but using pressures • KSP= solubility product constant, this indicates how soluble a solid is in water • KSP = (C)c(D)d • Reactants are Solids so they are not included in the equation

  9. LeChâtlier’s Principle • A system in equilibrium, when disturbed, will shift to the extent necessary to restore equilibrium • Example: • N2 + 3H2 2NH3 + 94K • Disturbance add N2: reactant is increased so product is increased, shift right • Disturbance increase temp: tries to lower energy, lower products, shift left • Disturbance increase pressure: will favor side with fewer moles, fewer moles on product side, increase products, shift right • Disturbance add catalyst: reaction goes faster but no change to each side, no shift

  10. Predicting Formation of precipitates based on Ksp • Knet= Ksp x Kf • Kf = formation constant • Used in reactions with complex ions • Lower Ksp means it’s less soluble. The combination with a complex ion makes it more soluble (the Kf value times the Kspvalue is much larger than the original Kspvalue).

  11. Concentration Units • Cmolar = nsolute/Vsolution • Cmolal = nsolute /msolvent (kg) • Mass Percent = msolute /msolution • Mole Fraction = nsolute /nsolution • Volume Fraction = Vsolute /Vsolution • Parts Per Million (PPM) = msolute (mg) / msolvent (kg) ≈ msolute (mg) / msolution (kg) when mass of solute is small enough

  12. Henry’s Law • Sg = kHPg • The solubility of gas increases in direct proportion to the partial pressure above the solution

  13. ColligativeProperties • Boiling Point Elevation: Tb = iCmolalKb • i = Van’t Hoff Factor – when dissolved , # of particles the molecule breaks into (Ex. NaCl = 2) • Kb = Boiling point elevation constant • solutes make it harder for water molecules to vaporize, thus requiring more energy to boil • Freezing Point Depression: Tf = iCmolalKf • Kf = freezing point depression constant • solutes make it harder for water molecules to form an orderly crystalline structure

  14. Raoult’s Law (Vapor Pressure) • PA = XAPOA • PA = solution vapor pressure • XA = mole fraction of solvent (nsolvent/nsolution) • POA = solvent vapor pressure • Adding a non-volatile solute to a solution will lower the vapor pressure, thus raising the boiling point

  15. Osmosis • V = nRT •  = nRT/V = CmolarRT •  = osmotic pressure • R = 8.314 if pressure is in Pascals (Pa). R = 0.08206 if pressure is in atm • Pressure required to prevent osmosis by a solvent toward a solution with a higher solute concentration

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