Example 5.13b: Stepwise Calculation of \(\mathrm{ΔHf°}\) Using Hess’s Law

Calculate \(ΔH\) for the process:

\(\ce{N2(g)}\)\(\ce{ + }\)\(\ce{2O2(g)}\)\(\ce{->}\)\(\ce{2NO2(g)}\)\(\ce{ }\)

from the following information:

\(\ce{N2(g)}\)\(\ce{ + }\)\(\ce{O2(g)}\)\(\ce{->}\)\(\ce{2NO(g)}\)\(\ce{ }\)       \(ΔH\) \( = 180.5\ \frac{\mathrm{kJ}}{\mathrm{mol}}\)

\(\ce{NO(g)}\)\(\ce{ + }\)\(\ce{1/2O2(g)}\)\(\ce{->}\)\(\ce{NO2(g)}\)\(\ce{ }\)       \(ΔH\) \( = - 57.06\ \frac{\mathrm{kJ}}{\mathrm{mol}}\)