Chem unit 6

• The Solution Process


  1. Separation of solvent molecules

  2. Separation of solute particles

  3. The solute and solvent molecules mix
• Endothermic process


  AH > 0
• Exothermic or endothermic process

  AH > 0 or AH < 0
• A solution can be formed by chemical or physical means
• Dissolving salt in water

  • Physical change
• Reaction between NaOH and HCl

  • Chemical change
• Heat of solution (ΔH)


  The amount of energy absorbed or released when a solution is formed
• Solvation

  The process in which the solvent molecules surround the solute particles
• Hydration

  Solvation when the solvent is water
• Types of intermolecular forces involved in dissolution

  • Ion-dipole forces
  • Hydrogen bonding
  • Dipole-dipole forces
  • Ion-induced dipole forces
  • Dipole-induced dipole forces
  • Dispersion forces
• Rate of dissolution


  • Affected by interparticle forces (intermolecular forces)
  • Affected by temperature
  • Affected by surface area
• Like dissolves like principle

  Polar dissolves polar, non-polar dissolves non-polar
• Miscible liquids


  • Water and ethanol (hydrogen bonding)
  • Benzene and oil (London dispersion force)
• Soluble solids


  • Polar solids in polar solvents
  • Non-polar solids in non-polar solvents
  • Iodine in benzene (London dispersion force)
  • Sugar in water (hydrogen bonding)
  • Sodium chloride in water (ion-dipole force)
• Solubility of ionic compounds

  • Affected by hydration energy
  • Affected by lattice energy
• Hydration energy


  Energy released when water molecules surround the ions of a salt
• Lattice energy


  Energy required to break one mole of an ionic solid into isolated gaseous ions
• Types of solutions based on equilibrium

  • Saturated solution
  • Unsaturated solution
  • Supersaturated solution
• Saturated solution


  Solution at equilibrium that contains the maximum amount of dissolved solute at a given temperature
• Unsaturated solution


  Solution that contains less than the equilibrium concentration of dissolved solute
• Supersaturated solution


  Solution that contains more than the equilibrium concentration of dissolved solute
• Supersaturated solutions can be prepared from saturated solutions if the solute is more soluble at higher temperatures
• As temperature increases


  Solubility of most solids increases
• As temperature increases


  Solubility of some solids increases up to a certain temperature and then decreases at higher temperatures
• Solubility of some ionic compounds

  • NaNO3
  • KMnO4
  • NaCl
  • K2SO4
  • KCl
• For gaseous solutes


  Increasing temperature decreases solubility
• As pressure increases


  Solubility of gases increases
• Henry's law


  The solubility of a gas (Cg) is directly proportional to the partial pressure of the gas (Pg) above the solution
• Cg = K * Pg


  • Where K is Henry's law constant
• Pressure has little effect on the solubility of liquids and solids
• Iodine in benzene (London dispersion force)


  Iodine is a non-polar solid that dissolves in benzene, a non-polar solvent. This is due to the London dispersion forces between the iodine molecules and the benzene molecules. These forces are weak intermolecular attractions that result from the temporary dipoles that form when electrons move around in a molecule.
• Temperature and solubility


  As temperature increases, the solubility of some solids can increase up to a certain point. Beyond that point, further increases in temperature can cause the solubility to decrease.