GEN CHEM 2

• Liquid-Vapor Equilibrium


  1. Convert liquid to gas by overcoming intermolecular forces with energy (molar heat of vaporization)

  2. Intermolecular forces vary between substances, so molar heat of vaporization is not the same
• Liquid-Solid Equilibrium


  1. ∆Hfus is always positive, molar heat of freezing (∆Hfreeze) is equal in magnitude but opposite in sign to ∆Hfus

  2. Intermolecular forces, melting points, and molar heats of fusion for some substances
• Sublimation

  • Process of converting solid to gas, reverse process is deposition
  • Molar heat of sublimation (∆Hsub) is the energy required to sublime 1 mole of a solid, equal to the sum of molar heats of vaporization and fusion
• Solution


  Homogenous mixture of two or more substances, with solute being the dissolved substance and solvent being the dissolving medium
• Classification of Solutions


  • Saturated - maximum solute dissolved
  • Unsaturated - less than maximum solute
  • Supersaturated - more solute than solvent can hold
• Solubility


  Maximum amount of solute dissolved in a given amount of solvent at a specific temperature
• Solubility Terms


  • Soluble - dissolves into another substance
  • Insoluble - inability to form a solution
  • Miscible - liquids soluble to each other
  • Immiscible - liquids that do not mix and form separate layers
  • Aqueous solution - solvent is water
• Factors affecting solubility


  • Nature of solute and solvent - "like dissolves like"
  • Temperature - affects solubility of solids and gases
• Solubility of solid and temperature

  • For many solutes, solubility increases with temperature
  • Some solutes like NaCl are not affected by temperature
  • Some solutes like Na2SO4 become less soluble as temperature increases
• Solubility of gas and temperature

  Gaseous solutes require lower temperature for higher solubility
• Solubility of gas in liquid

  Directly proportional to pressure, as described by Henry's Law
• Percent by volume


  Ratio of volume of solute to volume of solution, multiplied by 100
• Diluted


  Low amount of solute, use ppm (parts per million)
• Concentrated


  Large amount of solute, use ppb (parts per billion)
• Mole fraction


  Mole ratio between solute and solution, or between solvent and solution
• Molality (m)


  Moles of solute per kilogram of solvent
• Molarity (M)


  Moles of solute per liter of solution
• Liquids with strong intermolecular forces have high molar heats of vaporization
• Condensation requires heat release, and has negative heat change (∆Hcond) equal in magnitude to ∆Hvap.
• At equilibrium, the rate of evaporation equals the rate of condensation