Chemical Thermodynamics Question 487

Question: Calculate the heat change in the reaction 4,NH3(g)+3O2(g)2N2(g)+6H2O() at 298 K, given that the heats of formation at 298 K for NH3(g) and H2O() are - 46.0 and - 28.60 kJ mol1 respectively.

Options:

A) - 1861 kJ

B) - 1361 kJ

C) - 1261 kJ

D) - 1532 kJ

Show Answer

Answer:

Correct Answer: D

Solution:

  • ΔHo for the reaction 4NH3(g)+3O2(g)6H2O(l)+2N2(g)

ΔHo=ΔHfo(products)ΔHfo(reactants)

=6Hfo[H2O(l)]+ΔHf[N2(g)]

4ΔH[NH3(g)]+3ΔHf[O2(g)]

ΔHfo[H2O(l)]=286.0kJmol1

ΔHfo[NH2(g)]=0 and ΔHfo[N2(g)]

= 0 (by convention) ΔHo=6(286)+2(0)4(46.0)+3(0)

=1716+184=1532,kJ



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