chem

• Specific property


  The ratio of any extensive property of system to that of the mass of the system
• Average specific value


  Also known as intensive property
• Specific volume


  V/m = v, m³/kg
• Internal energy


  U/m, J/kg
• Entropy


  A measure of the "disorder" of a system, the number of different microscopic states a system can be in, given that the system has a particular fixed composition, volume, energy, pressure, and temperature
• Entropy is sometimes confused with energy, although they are related quantities, they are distinct
• Energy measures the capability of an object or system to do work
• Entropy


  Boltzmann's constant (k) x logarithm of number of possible states (Ω)
• Describe what happens when hydrochloric acid is added to magnesium oxide, calcium carbonate or aluminium oxide.
• Entropy

  The property of a system which measures the degree of disorder or randomness in the system
• Entropy


  A Greek word which means transformation
• Entropy


  Denoted by the symbol 's'
• Clausius was convinced of the significance of the ratio of heat delivered and the temperature at which it is delivered
• Entropy


  • It is the sum total of entropy due to positional disorder, vibrational disorder and configurational disorder, i.e. randomness due to change of state
• Entropy change


  Equal to the heat absorbed by the system divided by the temperature at which the change took place
• Change in entropy


  ΔS = δq/T
• This is the law expression for entropy change
• If the process is undergoing change at constant temperature, then ΔS = δq/T
• Entropy


  A thermodynamic property - a quantitative measure of disorder
• Entropy

  • Traces out its origin in molecular movement
  • Interpreted by Rudolf Clausius in 1850
  • Concept related to thermodynamic laws (2nd law of thermodynamics)
• Entropy


  Can be visualised due to processes like expansion, heating, mixing and reaction
• Entropy


  Associated with heat and temperature
• Types of Disorder

  • Positional disorder
  • Vibrational disorder (thermal disorder)
  • Configurational disorder
• Positional disorder

  Whether the atoms are free to move or not
• Vibrational disorder

  Whether the atoms vibrate about an average position
• Configurational disorder

  Distribution of different atoms or sites in a lattice
• Second Law of Thermodynamics

  States that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. In other words, the entropy of an isolated system will always increase over time.
• Acids


  Common both in nature and in the laboratory, have a sour taste and cause certain dyes to change colour
• Bases


  Common both in nature and in the laboratory, have a bitter taste and feel slippery (soap is a good example)
• By 1830 it was evident that all acids contain hydrogen but not all hydrogen containing substances are acids
• Arrhenius definition of acids

  Substances that produce hydrogen ions in water
• Arrhenius definition of bases

  Substances that produce OH- ions in water
• Arrhenius acid


  • Hydrogen chloride gas, which is highly soluble in water
• Hydrogen chloride gas dissolving in water

  HCl(g) + H2O → H+(aq) + Cl-(aq)
• The Arrhenius concept of acids and bases is rather limited as it is restricted to aqueous solutions
• Bronsted-Lowry definition of acids and bases

  Acid-base reactions involve the transfer of H+ ions from one substance to another
• The Bronsted-Lowry definition of acids and bases is more general than the Arrhenius definition
• Acids and bases are common both in nature and in the laboratory
• From the earliest days of experimental chemistry, scientists have recognized acids and bases by their characteristic properties
• Acids


  • Have a sour taste
  • Cause certain dyes to change colour