Question

Arrange the following in increasing order of lattice energy:

$LiCl,NaCl,KCl,RbCl,CsCl$
A) $CsCl<RbCl<KCl<NaCl<LiCl$
B) $LiCl<RbCl<KCl<NaCl<CsCl$
C) $LiCl<NaCl<KCl<RbCl<CsCl$
D) None of these

Answer 1

Hint: Lattice energy of a crystalline solid is defined as the energy released when two oppositely charged ions in their gaseous state combine to form a crystal lattice of that solid. Its value depends upon charge and size of ions present in the ionic compound.
Complete step by step answer:
Formation of ionic compound always have a negative enthalpy that means heat is released whenever two oppositely charge ions are brought together to form an ionic compound
Now the energy which gets released is termed as lattice energy and is use to determine the stability of a crystalline solid
More is the magnitude of lattice energy released more is the stability of the ionic compound
As in the above question we can see all the cation part of the compounds are the members of group one in periodic table and are termed as alkali metal which are highly electropositive
While the anion part in the question is same for all ionic compound that is chlorine which is a non-metal belonging to group seventeen of periodic table called halogens
Lattice energy is directly proportional to the charge on ion and as we can see that charge on all the ions of the question is$+1$ hence considering charge on ion it seems they all have same lattice energy but this is not true
As lattice energy also have an inverse relation with size of ion that means as size of ion increases lattice energy decreases.
 And we all know that down the group size of ion increases due to increase in the number of shell leading to decrease in lattice energy
$Cs>Rb>K>Na>Li$ (Size of ion)
$CsCl<RbCl<KCl<NaCl<LiCl$ (Order of lattice energy)
Hence option ‘A’ is the correct solution for the given question.

Note:
Lattice energy is extensively used in the evaluation and assessment of electron relationships and fluoride relationships. It is also used in the calculation of standard enthalpies of formation and to measure the strength of ionic acids.