Chemistry

• Colligative properties

  Properties that depend only on the number of solute particles present, not on the identity of the solute particles
• Colligative properties

  • Vapor pressure lowering
  • Boiling point elevation
  • Freezing point depression
  • Osmotic pressure
• Vapor pressure


  The vapor pressure of a solution with a non-volatile solute is always lower than that of the pure solvent
• Vapor pressure of a solution

  Depends on the concentration of the solute
• Raoult's Law


  The decrease in vapor pressure is directly proportional to the solute concentration
• Boiling point


  The temperature at which the vapour pressure of liquid becomes equal to the atmospheric pressure
• Boiling point


  Increases with external pressure
• Liquids with greater intermolecular forces

  Have high boiling point
• Adding a non-volatile solute to a solvent

  Lowers the vapour pressure
• To boil a solution

  The temperature has to be raised further to make its vapour pressure equal to atmospheric pressure
• Freezing point


  The temperature at which liquid state is converted into a solid state
• Pressure


  Increases freezing point
• Freezing point of a liquid


  The temperature at which the vapour pressure of solid is equal to the vapour pressure of liquid
• Freezing point depression


  A colligative property observed in solutions that results from the introduction of solute molecules to a solvent
• Freezing points of solutions

  Are all lower than that of the pure solvent and is directly proportional to the molality of the solute
• Freezing point depression


  The difference in temperature between the freezing point of the pure solvent and that of the solution
• Osmosis


  The movement of water or other solvent through a plasma membrane from a region of low solute concentration to a region of high solute concentration
• Reverse Osmosis


  A Technique for purifying water, in which pressure is applied to force liquid through a semipermeable membrane in the opposite direction to that in normal osmosis
• Semipermeable membrane


  A barrier that will only allow some molecules to pass through while blocking the passage of other molecules
• Thermochemistry


  The study of energy or heat flow that accompanies a chemical reaction and/or physical transformations
• Heat


  A form of energy transfer between two objects as a result of their difference in temperature
• Temperature


  The measurement of the hotness of coldness of an object
• Heat flow


  Generally from hotter object to a cooler one until thermal equilibrium is reached
• System


  The part of the universe being studied or to which the attention is focused
• Surroundings

  Everything else in the universe
• Endothermic process


  Heat is absorbed by a system
• Endothermic processes


  • Melting Ice, Photosynthesis of plants
• Exothermic process


  Heat is released by a system
• Exothermic processes


  • Freezing, Burning of fuel
• Heat (q)

  System to surroundings, heat is negative. Surroundings to system, heat is positive
• First Law of Thermodynamics

  The change in energy of a system is equal to the heat absorbed (q) by the system and the work (w) done on it
• Energy can neither be created nor destroyed, it can only be transferred between the system and the surroundings
• When work is done on the system

  It gains energy (+w)
• When work is done by the system

  It uses or transfers some energy (-w)
• System absorbs heat

  (+q)
• System releases heat

  (-q)
• Sample problem

  1. A gas releases 35J of heat as 84J of work was done to compress it

  ∆E = q + w

  ∆E = (-35J) + (84J)

  ∆E = +49J