Calculate the enthalpy of formation of ammonia from the following bond energy data: (N−N) bond =398kJmol−1; (H−H) bond =435kJmol−1 and(N≡N) bond =945.36kJmol−1.
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Solution
ΔH=[ΔH(N≡N)+3×ΔH(H−H)]−[6ΔH(N−H)] 945+3×435.0−6×389.0=−83.64kJ Heat formation of NH3=ΔH2=−83.642=−41.82kJmol−1