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 – metallic – ionic – Covalent Bond (network) – certain C-family elements and compounds

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

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

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

Solubility The amount of substance that can be dissolved in a solvent at a given temperature (g/L) Some Simple Solubility Rules – NO 3 - is always soluble – C 2 H 3 O 2 - is always soluble – OH - is insoluble with everything except alkali metals, NH 4 +, Ca 2+, Sr 2+, and Ba 2+ – PO 4 3- is insoluble with everything except alkali metals and NH 4 +

Equilibrium aA + bB  cC + dD Occurs when opposing reactions proceed at equal rates with constant concentrations K C = equilibrium constant – K C = {[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 Left, Q = K  Equilibrium Established No solids or liquids included in equation

Equilibrium continued K P = K C (RT) -  n or same expression as K c, but using pressures K SP = solubility product constant, this indicates how soluble a solid is in water – K SP = (C) c (D) d – Reactants are Solids so they are not included in the equation

LeChâtlier’s Principle A system in equilibrium, when disturbed, will shift to the extent necessary to restore equilibrium Example: – N 2 + 3H 2 2NH K Disturbance add N 2 : 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

Predicting Formation of precipitates based on K sp – K net = K sp x K f K f = formation constant – Used in reactions with complex ions – Lower K sp means it’s less soluble. The combination with a complex ion makes it more soluble (the K f value times the K sp value is much larger than the original K sp value).

Concentration Units – C molar = n solute /V solution – C molal = n solute /m solvent (kg) – Mass Percent = m solute /m solution – Mole Fraction = n solute /n solution – Volume Fraction = V solute /V solution – Parts Per Million (PPM) = m solute (mg) / m solvent (kg) ≈ m solute (mg) / m solution (kg) when mass of solute is small enough

Henry’s Law – S g = k H P g – The solubility of gas increases in direct proportion to the partial pressure above the solution

Colligative Properties – Boiling Point Elevation:  T b = iC molal K b i = Van’t Hoff Factor – when dissolved, # of particles the molecule breaks into (Ex. NaCl = 2) K b = Boiling point elevation constant solutes make it harder for water molecules to vaporize, thus requiring more energy to boil – Freezing Point Depression:  T f = iC molal K f K f = freezing point depression constant solutes make it harder for water molecules to form an orderly crystalline structure

Raoult’s Law (Vapor Pressure) – P A = X A P O A – P A = solution vapor pressure – X A = mole fraction of solvent (n solvent /n solution ) – P O A = solvent vapor pressure – Adding a non-volatile solute to a solution will lower the vapor pressure, thus raising the boiling point

Osmosis –  V = nRT –  = nRT/V = C molar RT  = osmotic pressure R = if pressure is in Pascals (Pa). R = if pressure is in atm – Pressure required to prevent osmosis by a solvent toward a solution with a higher solute concentration