Module 5.2.1- Lattice enthalpy

• Lattice enthalpy


  formation of one mole of an ionic compound from its gaseous ions under standard conditions

  
• Lattice enthalpy is a measure of the ___________ of _________ bonding in a giant ionic lattice

  strength, ionic
• First ionisation energy (revision)


  The removal of 1 mole of electrons from 1 mole of gaseous atoms
• Enthalpy change of formation (revision)


  the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
• Born-Haber cycle


  An enthalpy cycle that allows you to calculate the lattice enthalpy change of formation for system.There are 2 routes which you can take:

  Route 1: enthalpy change of formation

  Route 2: enthalpy change of atomisation, ionisation and lattice enthalpy

  
• Standard enthalpy change of atomisation (do not need to remember)


  The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.example: Na(s) -> Na(g)
• 1st electron affinity (do not need to remember)


  The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

  example: Cl(g) + e- -> Cl-(g)
• Successive electron affinities


  The second successive electron affinity is endothermic

  
• Standard enthalpy change of solution


  The enthalpy change that takes place when one mole of a solute is completely dissolved in a solvent (water usually) under standard conditions

  
• Experimental determination of the enthalpy change of solution

  
• Enthalpy change of hydration


  The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

  
• Lattice enthalpy energy cycle (with enthalpy change of hydration)

  4 ARROWS!

  
• 2 factors affecting lattice enthalpy

  ionic size ionic charge
• The effect of increasing ionic size on lattice enthalpy

  ionic radius increases attraction between ions decrease lattice energy less negative melting point decreases becomes less exothermic

  
• The effect of increasing ionic charge on lattice enthalpy

  ionic charge increases attraction between ions increases lattice energy becomes more negative melting point increases becomes more exothermic
• The effect of increasing ionic charge on hydration enthalpy

  ionic charges increases attraction with water molecules increases hydration energy becomes more negative becomes more exothermic
• The effect of increasing ionic size on hydration enthalpy

  ionic radius increases attraction between ion and water molecules decreases hydration energy becomes less negative becomes less exothermic