Born Haber cycle

• enthalpy change is heat energy change at constant pressure
• standard conditions are: 298K and 100kPa and all substances are present in their standard states
• ions in lattices are held together by ionic bonds so it takes energy to break apart bonds and energy is given out when new bonds form (same amount of energy)
• lattice enthalpy is a measure of ionic bond strength and have specific values that differ depending on the ions involved
• lattice formation enthalpy is the enthalpy change when 1 mole of a solid iconic compound is formed from from its gaseous ions
• lattice dissociation enthalpy is the enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions
• Enthalpy change of formation is when 1 mole of a compound is formed from its elements in their standard states under standard conditions
• Bond dissociation enthalpy is when all the bonds of the same type in 1 mole of gaseous molecules are broken

  • Cl2 (g) ---> 2Cl (g)
• Enthalpy change of atomisation of a compound the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state

  • NaCl (s) ---> Na (g) + Cl (g)
• First ionisation energy is the amount of energy required to remove 1 electron from 1 mole of gaseous atoms to form 1 mole of ions with 1+ charge

  • Mg (g) ---> Mg+ (g) + e-
• second ionisation energy is the amount of energy required to remove 1 electron from 1 mole of gaseous 1+ ions to form 1 mole of 2+ ions

  • Mg+ (g) ---> Mg2+ (g) + e-
• First electron affinity is when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

  • O (g) + e- ---> O- (g)
• Second electron affinity is when 1 mole of gaseous 2- ions is made from 1 mole of gaseous 1- ions

  • O- (g) + e- ---> O2- (g)
• Enthalpy change of hydration is when 1 mole of aqueous ion is formed from gaseous ions

  • Na+ (g) ---> Na+ (ag)
• Enthalpy change of solution is when 1 mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution
• enthalpy of a solution = enthalpy of lattice formation + ∑ hydration enthalpies
• the value for lattice formation is always negative (-) and is the same value as lattice disassociation but positive (+)
• enthalpy of a solution = (+) dissociation enthalpy OR (-) formation enthalpy + (hydration enthalpy of ion x number of atoms) + (hydration enthalpy of ion 2 x number of atoms)
• enthalpy change of solution:

  A) solution

  B) lattice

  C) x2

  
• THINGS TO REMEMBER DOING BORN-HABER CYCLES

  • Group 2 metal = 1st and second ionisation energies 
  • Anything with 2 after it but single charge e.g Cl2 = 2x atomisation energy and 2x 1st electron affinity