Energy

• Equation used to calculate entropy change is ΔG = ΔH - TΔS
• Temperature affects entropy by

  The greater the temperature, the more energy particles have and the more they move, leading to a more random arrangement of particles and higher entropy
• When a solid ionic lattice is dissolved in solution

  Entropy increases because the ions become more disordered
• Symbol of entropy is S
• Gas is more disordered than solid
• Unit of standard entropy is J K-1 mol-1
• Change in number of gas molecules in a reaction affects entropy by


  Increase in number of gas molecules leads to an increase in entropy. Decrease in number of gas molecules leads to a decrease in entropy
• ΔH

  Change in enthalpy
• Feasibility of spontaneous change

  Positive: negative
• Feasibility of spontaneous change

  Negative: Negative at low temperatures, Reaction feasible at low temperature
• Gibbs’ free energy equation

  ΔG = ΔH - TΔS
• Reaction may have high activation energy
• Rate of reaction may be very slow
• Feasibility of spontaneous change

  Negative: Negative
• ΔG

  Gibbs’ free energy
• ΔS

  Change in entropy
• What are the limitations of the predictions of feasibility made by using ΔG? (2)
• Feasibility of spontaneous change

  Negative: positive
• For a reaction to occur spontaneously, ΔG must be positive or negative
• Feasibility of spontaneous change

  Positive: positive
• Hydration

  When an ionic lattice is broken, the ions become part of the solution. Positive ions get attracted towards slightly negative oxygen and negative ions get attracted towards slightly positive hydrogen
• What does a more exothermic lattice enthalpy mean?
• Which ions have more negative lattice enthalpy values? Smaller / larger ions? Why?
• Why is it not possible to measure lattice enthalpy directly?
• Factors impacting the magnitude of the enthalpy of hydration

  • Size of the ion
  • Charge on the ions
• What are the factors that impact the size of lattice enthalpy?
• Factors impacting the size of lattice enthalpy

  • Size of ions involved
  • Charges on the ions
  • Ionic bond strength
• What are the factors that impact the magnitude of the enthalpy of hydration?
• Smaller ions have more negative lattice enthalpy values because they can get closer, hence more stronger attraction
• It is not possible to form 1 mole of ionic solid from its gaseous ions
• More exothermic lattice enthalpy means more stronger ionic bonds