THERMODYNAMICS
LATTICE ENTHALPY
Formation of 1 mole of ionic lattice from its gaseous ions under standard conditions
Exothermic: ionic bond formation
To measure strength of ionic bonding in a giant ionic lattice
IONIC SIZE increases :
● Attraction between ions decreases
● Lattice enthalpy less negative
Across period ionic size decreases: more protons attract same number of electrons
IONIC CHARGE increases:
● Attraction between ions increases
● Lattice enthalpy more negative
Outweighs increase in the number of ions with positive charge
ENTHALPY CHANGES OF:
ATOMISATION: formation of 1 mole of gaseous atoms from the element in its standard
state under standard conditions
Endothermic: bonds are broken to form gaseous atoms
FIRST IONISATION ENERGY: the energy required to remove one mole of the most
loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous
ions each with a charge of 1+
Endothermic: energy is required to overcome the attraction between the negatively
charged electron and the positively charged nucleus
FIRST ELECTRON AFFINITY: 1 electron is added to each atom in 1 mole of gaseous
atoms to form 1 mole of gaseous 1- ions
Exothermic: electron being added is attracted to the positive nucleus
SECOND ELECTRON AFFINITY:
Endothermic: the second electron is being gained by the anion that repels the electron
away = energy is required to force the negative electron onto the negative ion
BORN-HABER CYCLES
Enthalpy of formation = sum of known enthalpy changes
LATTICE ENTHALPY
Formation of 1 mole of ionic lattice from its gaseous ions under standard conditions
Exothermic: ionic bond formation
To measure strength of ionic bonding in a giant ionic lattice
IONIC SIZE increases :
● Attraction between ions decreases
● Lattice enthalpy less negative
Across period ionic size decreases: more protons attract same number of electrons
IONIC CHARGE increases:
● Attraction between ions increases
● Lattice enthalpy more negative
Outweighs increase in the number of ions with positive charge
ENTHALPY CHANGES OF:
ATOMISATION: formation of 1 mole of gaseous atoms from the element in its standard
state under standard conditions
Endothermic: bonds are broken to form gaseous atoms
FIRST IONISATION ENERGY: the energy required to remove one mole of the most
loosely held electrons from one mole of gaseous atoms to produce 1 mole of gaseous
ions each with a charge of 1+
Endothermic: energy is required to overcome the attraction between the negatively
charged electron and the positively charged nucleus
FIRST ELECTRON AFFINITY: 1 electron is added to each atom in 1 mole of gaseous
atoms to form 1 mole of gaseous 1- ions
Exothermic: electron being added is attracted to the positive nucleus
SECOND ELECTRON AFFINITY:
Endothermic: the second electron is being gained by the anion that repels the electron
away = energy is required to force the negative electron onto the negative ion
BORN-HABER CYCLES
Enthalpy of formation = sum of known enthalpy changes
