Thermodynamics

• What are Born-Haber cycles used for?


  To determine enthalpy changes that cannot be measured directly
• What are lattice enthalpies used for?


  They are used for ionic substances
• What is lattice dissociation enthalpy?


  The energy required to break apart an ionic lattice into gaseous ions
• How is lattice formation enthalpy defined?


  It is the energy required to form an ionic lattice from gaseous ions
• What is atomisation enthalpy?


  The energy required for the formation of a mole of gaseous atoms
• What does the enthalpy of electron affinity represent?

  The enthalpy change when one mole of 1- gaseous ions is formed from 1 mole of gaseous atoms
• How is the lattice enthalpy of formation calculated in a Born-Haber cycle?


  By following the cycle from the start of the arrow to the head
• What is the enthalpy of solution?


  The enthalpy change when one mole of ionic solid is dissolved in water
• How is the enthalpy of hydration defined?


  It is the enthalpy change when one mole of gaseous ions is dissolved in water
• Why is the enthalpy of hydration usually negative?


  Because water attracts negative ions due to its partial positive region
• What assumptions does the perfect ionic model make?

  • All ions are perfectly spherical
  • Ions display no covalent character
• What is entropy a measure of?


  It is a measure of disorder in a system
• How does temperature affect entropy?


  Entropy increases as temperature increases
• Which state of matter has the greatest entropy?


  Gases
• What is the relationship between spontaneous reactions and entropy?


  All spontaneous reactions have a positive entropy value
• What does a negative ∆G indicate?


  It indicates that the reaction is spontaneous
• How does temperature affect the feasibility of a reaction?


  Changing the temperature can change the feasibility of the reaction
• What is lattice enthalpy?

  Energy required to break ionic solid
• What are the two types of lattice enthalpy?

  Theoretical and experimental lattice enthalpy
• How is theoretical lattice enthalpy calculated?

  Using a model based on Coulomb's law
• What assumptions does the theoretical lattice enthalpy model make?

  Assumes perfect ionic bonding and point charges
• What is the Born-Haber cycle used for?

  To determine theoretical lattice enthalpy
• What ideal conditions does theoretical lattice enthalpy assume?

  Perfectly spherical ions with no repulsions
• What does theoretical lattice enthalpy not account for?

  Real-world complexities like covalent character
• How is experimental lattice enthalpy measured?

  Using calorimetry or derived data
• What does experimental lattice enthalpy reflect?

  Actual energy change during dissolution
• What factors does experimental lattice enthalpy take into account?

  Ion size, charge distribution, non-ideal interactions
• What is the key difference between theoretical and experimental lattice enthalpy?

  Theoretical is idealized; experimental is real
• What are the two compounds compared in the study?

  MgI₂ and NaCl
• What is the theoretical lattice enthalpy of MgI₂ based on?

  • Consists of Mg²⁺ and I⁻ ions
  • Strong electrostatic attraction due to high charge and small size of Mg²⁺
  • Large lattice enthalpy predicted by Coulomb’s law
• Why is the theoretical lattice enthalpy of MgI₂ expected to be high?

  Due to strong electrostatic attraction between ions
• What ions make up Magnesium Iodide (MgI₂)?

  Mg²⁺ and I⁻ ions
• What factors cause the experimental lattice enthalpy of MgI₂ to be lower than the theoretical value?

  Ion polarizability and covalent character
• How does ion polarizability affect the lattice enthalpy of MgI₂?

  It weakens the ionic bond in the lattice
• What is the covalent character in MgI₂'s bonding?

  Some degree of covalent bonding between ions
• What is the theoretical lattice enthalpy of NaCl based on?

  • Consists of Na⁺ and Cl⁻ ions
  • Smaller and less charged Na⁺ compared to Mg²⁺
  • Moderate lattice enthalpy due to lower charges and larger distances
• Why is the theoretical lattice enthalpy of NaCl expected to be moderate?

  Lower ion charges and larger distances between ions
• What ions make up Sodium Chloride (NaCl)?

  Na⁺ and Cl⁻ ions
• What factors cause the experimental lattice enthalpy of NaCl to be slightly lower than the theoretical value?

  Ion pairing and lattice defects
• How does NaCl's ionic nature affect its lattice enthalpy compared to MgI₂?

  NaCl has a more consistent match between values