71-163 kJ (2) OTR 13. The standard ...
Question

# 71-163 kJ (2) OTR 13. The standard enthalphy of formation of NH3 is 46.0 kJ moll. If the enthalpy of formation of H2 from its atoms is -436 kJ mol-' and that of N2 is -712kJ mol!, the average bond enthalpy of AIEEE-2010) N-H bond in NH3 is :- (3) + 352 kJ mol (4) +1056 ku mor (1)-1102 kJ mol' (2) -964 kJ mol'

JEE/Engineering Exams
Chemistry
Solution
121
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( mathrm{NH}_{3}(mathrm{g}) longrightarrow frac{1}{2} mathrm{N}_{2}(mathrm{g})+frac{3}{2} mathrm{H}_{2}(mathrm{g}) ) ( Delta mathrm{H}^{circ}=-Delta-mathrm{H}_{mathrm{f}}^{circ}left(mathrm{NH}_{3}right)=-(-46)=46 mathrm{k} mathrm{mol}^{-1} ) ( mathrm{AJs}_{0}, Delta mathrm{H}^{circ}=3 Delta mathrm{H}_{mathrm{N}-mathrm{H}}+frac{1}{2} Delta mathrm{H}_{mathrm{N} equiv mathrm{N}}+frac{3}{2} Delta mathrm{H}_{mathrm{H}-mathrm{H}} ) ( 46=3 Delta mathrm{H}_{mathrm{N}-mathrm{H}}+frac{1}{2}(-712)+frac{3}{2}(-436) ) ( Delta mathrm{H}_{mathrm{N}-mathrm{H}}=frac{1}{3}[1056]=+352 mathrm{kJ} mathrm{mol}^{-1} ) ( mathrm{NH}_{3}(mathrm{g}) longrightarrow frac{1}{2} mathrm{N}_{2}(mathrm{g})+frac{3}{2} mathrm{H}_{2}(mathrm{g}) ) ( Delta mathrm{H}^{circ}=-Delta-mathrm{H}_{mathrm{f}}^{circ}left(mathrm{NH}_{3}right)=-(-46)=46 mathrm{kJ} mathrm{mol}^{-1} ) ( mathrm{AJs}_{0}, Delta mathrm{H}^{circ}=3 Delta mathrm{H}_{mathrm{N}-mathrm{H}}+frac{1}{2} Delta mathrm{H}_{mathrm{N} equiv mathrm{N}}+frac{3}{2} Delta mathrm{H}_{mathrm{H}-mathrm{H}} ) ( 46=3 Delta mathrm{H}_{mathrm{N}-mathrm{H}}+frac{1}{2}(-712)+frac{3}{2}(-436) ) ( Delta mathrm{H}_{mathrm{N}-mathrm{H}}=frac{1}{3}[1056]=+352 mathrm{kJ} mathrm{mol}^{-1} )