The standard enthalpy of atomisation of PCl 3 ( g ) is 195 Kcal/mol. What will be the standard enthalpy of atomisation of PCl 5 ( g ) , if the bond dissociation energies of axial P-Cl bonds in PCl

Question

The standard enthalpy of atomisation of PCl 3 ​ ( g ) is 195 Kcal/mol. What will be the standard enthalpy of atomisation of PCl 5 ​ ( g ) , if the bond dissociation energies of axial P-Cl bonds in PCl 5 ​ ( g ) are 10\% lesser and the bond dissociation energies of equatorial P − Cl bonds in PCl 5 ​ ( g ) are 10% higher than the bond dissociation energies of P − Cl bonds in PCl 3 ​ ( g ) .

TestHub · Accepted Answer

Let D be the average P-Cl bond dissociation energy in PCl₃(g). Enthalpy of atomisation of PCl₃ = 3 D = 195 Kcal/mol. So, D = 195/3 = 65 Kcal/mol. In PCl₅(g), there are 3 equatorial and 2 axial P-Cl bonds. Equatorial bond energy = 1.10 D = 1.10 × 65 = 71.5 Kcal/mol. Axial bond energy = 0.90 D = 0.90 × 65 = 58.5 Kcal/mol. Enthalpy of atomisation of PCl₅ = 3 × ( 71.5 ) + 2 × ( 58.5 ) = 214.5 + 117 = 331.5 Kcal/mol.

Chemistry - Thermochemistry Question with Solution | TestHub

Options:

Doubts & Discussion