The lattice energy of solid NaCl is 180 kcal / mol . The dissolution of the solid in water in the form of ions is endothermic to the extent of 1 kcal / mol . If the solution energies of Na + and Cl −

Question

The lattice energy of solid NaCl is 180 kcal / mol . The dissolution of the solid in water in the form of ions is endothermic to the extent of 1 kcal / mol . If the solution energies of Na + and Cl − are in the ratio 6 : 5 , what is the enthalpy of hydration of Cl − ion?

TestHub · Accepted Answer

Na⁺(g) + Cl⁻(g) ⟶ NaCl(s) ; Δ H = 180 k c a l NaCl(s) + aq ⟶ Na⁺(aq) + Cl⁻(aq) ; Δ H = 1 k c a l Na⁺(g) + Cl⁻(g) + aq ⟶ Na⁺(aq) + Cl⁻(aq) ; Δ H = A k c a l Δ H so l u t i o n ​ = Δ H l a tt i ce ​ + Δ H h y d r a t i o n ​ 1 = 180 + Δ H h y d r a t i o n ​ Δ H h y d r a t i o n ​ = − 179 k c a l = A Δ H N a + ( h y d r a t i o n ) ​ + Δ H C l − ( h y d r a t i o n ) ​ = A Δ H C l − ( h y d r a t i o n ) ​ = 11 5 A ​ = 11 5 ( − 179 ) ​ = − 81.4 k c a l

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JEE Main + Advanced (1 year 12th class)