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Lattice energy
This is the enthalpy change when one mole of an ionic crystal is made from its constituent gaseous ions. It is always a large, negative value as energy is released when the oppositely charged ions attract each other. For example, the following equations show the processes involved in the lattice energies of sodium chloride and magnesium chloride respectively:
|
Na+(g) + Cl-(g) ⇒ NaCl(s) |
DH = - 780 kJ mol-1 |
|
Mg2+(g) + 2Cl-(g) ⇒ MgCl2(s) |
DH = - 2526 kJ mol-1 |
Notice that the lattice energy for magnesium chloride is much bigger than that for sodium chloride. Suggest why this is so, and check your answer here.