Entropy

• Entropy definition


  Measure of disorder in a system, The.number of ways energy can be shared out between particles, more disorder = higher level of energy
• Solids have the lowest Lebel of disorder, particles arranged neatly in rows, liquids and gases more disordered
• More moles produced = entropy increases, number of particles affect entropy
• • A reaction can be spontaneous (feasible) even is enthalpically unfavourable ( endothermic)
  • Increasing entropy is energetically favourable, some reactions enthalpically unfavourable (endothermic) can still spontaneously react if changes in entropy over come changes in enthalpy
• Example of a spontaneous endothermic reaction

  Ba(OH)2.8H2O (s) + 2NH4Cl (s) --> 2NH3 (g) + 1oH2O (l) + BaCl2 (s)

  Barium hydroxide + ammonium chloride

  1. this reaction is endothermic and enthalpically not favourable (+164kjmol-1)
  2. 3 moles of left and 13 moles moles on the right, entropically favourable, more moles produced = entropy increases
  3. Starts with two solids but produces gas and liquid, increasing disorder = entropically favourable
• Entropy change


  AS Jkmol-1 = Products - Reactants

  Entropy values given as standard

  • 1 mole of substance
  • 1000 kPa
  • 298K
• If entropy value is positive, the reaction is entropically feasible.