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Solution Formation

solution process - like molecules dissolve like molecules

  • ionic compounds dissolved in polar solvent (w/ ion-dipole forces)
  • covalent compounds dissolved in nonpolar solvent (w/ dispersion forces)
  • forces between solvent/solute must be greater than forces between solute molecules
  • solvation - dissolving solute w/ solvent (solvent molecules completely surround solute)
    • hydration - solvation when solvent is water
  • Hsoln = H1 + H2 + H3
    • H1 = separation of solute molecules (endothermic)
    • H2 = separation of solvent molecules (endothermic)
    • H3 = forming solvent-solute interactions (exothermic)
    • Hsoln can be either exothermic/endothermic
  • no solution if too endothermic, spontaneous reaction if exothermic

spontaneous solution formation - usually exothermic

  • energy decrease >> reaction starts spontaneously
  • entropy/disorder increase >> reaction starts spontaneously (even if endothermic)
  • molecules unrestrained >> spontaneous mixing occurs
  • no solution of solute-solute or solvent-solvent forces greater than solvent-solute forces
  • solute can change or remain unchanged after solvation

crystallization - opposite of solvation

  • saturated solution - will not dissolve more solute if added
  • solubility - amount of solute needed to form saturated solution
  • unsaturated solution - dissolves less solute than in saturated solution
  • supersaturated solution - contains more solute than needed for saturation
    • possible at different temperatures
    • very unstable, will crystallize w/ just a little bit of added solute

solute-solvent interactions - determines tendency of substances to mix

  • stronger solute-solvent interaction >> greater solubility
  • polar liquids dissolve polar solutes, don’t dissolve nonpolar solutes
  • miscible - describes substances that dissolve in each other
  • immiscible - describes substances that don’t dissolve in each other
  • increase # of polar groups >> increase solubility in water
Subject: 
Chemistry
Subject X2: 
Chemistry

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