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The lattice energy of NaCl, NaF, KCl and RbClfollow the order:
A. KCl<RbCl<NaCl<NaF
B. NaF<NaCl<KCl<RbCl
C. RbCl<KCl<NaCl<NaF
D. NaCl<RbCl<NaF<KCl

Answer
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Hint: Lattice energy: The amount of energy released when 1mole of an ionic solid is formed from its gaseous ions.

Complete step by step answer:
Lattice energy depends upon charge and size of cation.
Lattice energy is directly proportional to charge on ion i.e. larger the magnitude of charge on ions, greater will be the attractive forces, higher is the value of lattice energy and inversely proportional to size of an ion i.e. smaller the size of ions, lesser is the internuclear distance and greater will be the interionic attraction. Hence, more will be the value of lattice energy. The given ionic solids are NaCl, NaF, KCl,andRbCl.
In case of NaFand NaClas Fis small in size than Clthen NaFhas greater lattice energy than NaClbut in case of KCl, RbClas Na+is smaller than that of K+ion so NaClhas greater lattice energy than KCl and RbCl.
The order of lattice energy is NaF>NaCl>KCl>RbCl.

Hence, the correct option is (C).

Note:
The important consequence of the lattice energies are:
(i) The greater the lattice enthalpy, the more the stability of ionic compounds.
(ii) The lattice energy is greater for small, highly charged ions.
(iii) The lattice energy affects the solubility of the ionic compounds.