lattice energy of AlCl3 is X kcal.Calculate the lattice energy of Nacl.
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The lattice energy of solid NaCl is 180kcal per mol. The dissolution of the solid in water in the form of ions is endothermic to the extent of 1kcal per mol. If the solvation energies of Na
+
and Cl
−
ions are in the ratio 6:5, what is the enthalpy of hydration of sodium ion?
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ANSWER
Solution:- (B) −97.5kcal/mol
Given that:-
ΔH
dissolution
=1kcalmol
−1
ΔH
lattice
=180kcalmol
−1
Let ΔH
Na
+
and ΔH
Cl
−
be the solvation energy of sodium and chloride ion respectively.
ΔH
hydration
=?=ΔH
Na
+
+ΔH
Cl
−
Given that:-
ΔH
Cl
−
ΔH
Na
+
=
5
6
⇒ΔH
Cl
−
=
6
5
ΔH
Na
+
∴ΔH
hydration
=ΔH
Na
+
+
6
5
ΔH
Na
+
⇒ΔH
hydration
=
6
11
ΔH
Na
+
As we know that
ΔH
hydration
=ΔH
lattice
−ΔH
dissolution
6
11
ΔH
Na
+
=180−1
⇒ΔH
Na
+
=
11
6
×179=97.63KJmol
−1
≈97.5Kcalmol
−1