Question

A. The combustion reaction of nitromethane fuel occurs as follows: 2 CH3 NO2 (l) + 3/2...

A. The combustion reaction of nitromethane fuel occurs as follows: 2 CH3 NO2 (l) + 3/2 O2 (g) ? 2 CO2 (g) + 3 H2 O(l) + N2 (g) The standard enthalpy of this reaction is –1418 kJ. What is the standard enthalpy of formation of nitromethane in kJ/mol?

B. Use standard enthalpies of formation to calculate ? H ? ? rxn r x n for the following reaction: SO2 (g) + ½ O2 (g) ? SO3 (g)

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Answer #1
  1. The reaction is

2 CH3 NO2 (l) + 3/2 O2 (g) …………> 2 CO2 (g) + 3 H2 O(l) + N2 (g)   dHrxn = -1418 kJ

dHrxn = 2dHf(CO2) + 3dHf(H2O) + dHf(N2) – 2dHf(CH3NO2) – 3/2dHf(O2)

Using standard values,

=> -1418 = 2 x (-393.5) + 3 x (-241.8) + 0 -2dHf(CH3NO2) – 0 = -787 – 725.4 – 2dHf(CH3NO2)

=> dHf(CH3NO2) = -47.2

Hence, the enthalpy of formation of nitromethane is -47.2 kJ/mol.

  1. The reaction is

                             SO2 (g) + ½ O2 (g) …………….> SO3 (g)

dHrxn = dHf(SO3) – dHf(SO2) – ½ dHf(O2)

               = -395.7 + 296.8 – 0 = -98.9 kJ/mol

dHrxn = -98.8 kJ/mol

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