Module 5.2.2- Entropy

• Entropy


  a measure of the disorder of a system it is a measure of the dispersal of energy in a system
• In general, what are the levels of entropies compared to each other in different states


  Gas- highest entropy

  Liquid- lower entropy

  Solid- lowest entropy
• Units of entropy


  J K-1 mol-1
• When a substance goes from solid -> liquid -> gas the entropy increases since...


  ...melting and boiling increase the randomness of particles

  energy is spread out more and delta S is positive
• Change in the number of gaseous molecules- more gaseous particles


  When there are more gas molecules/gas molecules produced, entropy increases since the disorder of the particles are increased and energy is more spread out.
• Change in the number of gaseous molecules- less gaseous particles


  decrease in the randomness of particles. energy is spread out less and so delta S is negative
• Standard entropy


  The entropy of one mole of a substance under standard conditions (100kPa and 298K). They are always positive
• Standard entropy equation

  ΣS(products) - ΣS(reactants)

  
• Feasibility of a reaction


  the likelihood or not of a reaction occurring when reactants are mixed
• Free energy change


  the difference between the change in enthalpy and the product of the Kelvin temperature and the entropy change
• Gibbs free energy equation


  Δ G = Δ H - T Δ S .

  T= in Kelvin must be kJ K-1 mol-1
• Conditions for the feasibility of a reaction

  Δ G <= 0
• What must you always do when using the Gibbs equation

  Check units and convert to kJ K-1 mol-1

  Since ΔS is usually in J K-1 mol -1 it will need to be converted to kJ K-1 mol-1 by dividing by 1000.
• Feasibility differences at high and low temperatures

  
• Minimum temperature required for a reaction to take place equation(rearrange Gibb's equation)


  T = ΔH / ΔS
• Limitations of predictions made for feasibility


  Some reactions with a -ΔG value do not take place

  It does not take into account of the kinetics or the rate of reaction.