JEE Main2010ChemistryThermodynamics (C)Actual
The standard enthalpy of formation of NH ₃ is -46.0 ~kJ ~mol ⁻¹ . If the enthalpy of formation of H ₂ from its atoms is -436 ~kJ ~mol ⁻¹ and that of N ₂ is -712 ~kJ ~mol ⁻¹ , the average bond enthalpy of N - H bond in NH ₃ is
Options
- A-964 ~kJ ~mol ⁻¹
- B+352 ~kJ ~mol ⁻¹
- C+1056 ~kJ ~mol ⁻¹
- D-1102 ~kJ ~mol ⁻¹
Correct answer
B. +352 ~kJ ~mol ⁻¹
Step-by-step solution
Enthalpy of formation of NH ₃=-46 ~kJ / mole N ₂+3 H ₂ 2 NH ₃ H _ f =-2 46 ~kJ ~mol Bond breaking is endothermic and Bond formation is exothermic Assuming ' x ' is the bond energy of N - H bond ( kJ mol ⁻¹ ) aligned & 712+(3 436)-6 x =-46 2 & x =352 ~kJ / mol aligned