A level OCR Chemistry module 5.2

CHEMISTRY
MODULE 5 – PHYSICAL CHEMISTRY AND TRANSITION ELEMENTS
5.2 – ENERGY


5.2.1 – Lattice enthalpy

 Define the tem lattice enthalpy (ΔLEH)
o Is the enthalpy change when 1 mole of a solid ionic compound is
formed from its gaseous ions under standard conditions
o Lattice enthalpies are negative and can be used as a measure of the
strength of ionic bonding in a giant ionic lattice



 Define enthalpy change of formation
o The enthalpy change when1 mole of a compound is formed from its
elements under standard conditions, all reactants and products being in
their standard states



 Define enthalpy change of atomisation
o the enthalpy change when 1 mole of gaseous atoms is formed from the
element in its standard state



 Define first ionisation energy
o the enthalpy change required to remove 1 mole of electrons from 1
mole of gaseous atoms to form 1 mole of gaseous ions



 Define first electron affinity
o the enthalpy change that occurs when 1 mole of gaseous atoms gain 1
mole of electrons to form 1 mole of gaseous ions with a –1 charge
o The first electron affinity is exothermic for atoms form negative ions
because the ion is more stable than the atom and there is an attraction
between the nucleus and the electron



 Define second electron affinity
o The second electron affinity is the enthalpy change when one mole of
gaseous 1- ions gains one electron per ion to produce gaseous 2- ions
o The second electron affinity is endothermic because it take energy to
overcome the repulsive force between the negative ion and the electron