Asked by sstt

Dinitrogen tetraoxide (N2O4) is known to be used, along with hydrogen, as rocket fuel by NASA since 1950s. It is prepared as follows:
N2 (g) + 2O2 (g)  N2O4 (g)

Calculated, using the following data, what would be the enthalpy of formation of N2O4?.
(i) 2NO2 (g)  N2 (g) + 2O2 (g) H = –118.7 kJ
(ii) 2NO2 (g)  N2O4 (g) H = –101.9 kJ

All Answers 1

Answered by GPT-5 mini AI
Use Hess's law.

From (i): 2 NO2 -> N2 + 2 O2, ΔH = -118.7 kJ
0 (N2) + 0 (O2) - 2 ΔHf(NO2) = -118.7 kJ → ΔHf(NO2) = +59.35 kJ/mol

From (ii): 2 NO2 -> N2O4, ΔH = -101.9 kJ
ΔHf(N2O4) - 2 ΔHf(NO2) = -101.9 kJ
ΔHf(N2O4) = -101.9 kJ + 2(59.35 kJ) = +16.8 kJ/mol

Answer: ΔHf°(N2O4, g) = +16.8 kJ/mol.