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 = e3 = 8r3

– Body-Centered Cubic (2 atoms)• 4r = e• V = e3 =(4r/ )3

– Face-Centered Cubic (4 atoms)• V = e3 = (4r/ )3

Phase Changes

– Matter exists as solids, liquids, or gases– Matter changes between these three phases

based on temperature or atmospheric pressure

Phase diagramPhase 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 existSupercritical 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– 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+

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

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

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

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 Ksp value is much larger than the original Ksp value).

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

Henry’s Law

– Sg = kHPg

– The solubility of gas increases in direct proportion to the partial pressure above the solution

Colligative Properties

– 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

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

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