Name: Hybridisation in SF₆ Molecule
Uploaded: 2019-07-19
Duration: 2 min 31 s
Description: Understand the bonding present in the case of sulphur hexafluoride. This video illustrates that the hybridisation present in the case of sulphur hexafluoride...

Question

Define Lattice energy. On what factors do it depend? How does it help to predict the stability of the ionic compound formed?

Accepted Answer

Lattice Enthalpy: It is defined as the energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions. For example, the lattice enthalpy of $NaCl$ is $788 kJ {mol}^{- 1}$ . This means that $788 kJ$ of energy is required to separate one mole of solid $NaCl$ into one mole of ${Na}^{+} (g)$ and one mole of ${Cl}^{-} (g)$ to an infinite distance.

The value of lattice enthalpy depends upon the following factors:
(i) Charge on the Ions: Higher the charge on the ions, greater is the force of attraction and hence larger is the amount of energy released, e.g. Lattice enthalpies of some ionic compounds are in the order
$NaCl (- 758 kJ {mol}^{- 1}) < {CaCl}_{2} (- 2254 kJ {mol}^{- 1}) < MgO (- 3932 kJ {mol}^{- 1})$
(ii) Size of the Ions: Larger the size of ions, higher is the internuclear distance and lesser will be the force of attraction and hence lesser will be the lattice energy.
e.g. Lattice enthalpies of some ionic compounds follow the order as given below:
$NaCl (- 758 kJ {mol}^{- 1}) > NaBr (- 752 kJ {mol}^{- 1})$

Higher the value of lattice energy, higher is the ease of formation of ionic compound.

Define Lattice energy. On what factors do it depend? How does it help to predict the stability of the ionic compound formed?

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