Question

The combustion reaction of nitromethane fuel is given by: 2 CH₃NO₂(l) + 3/2 O₂(g) → 2 CO₂(g) + 3 H₂O(l) + N₂(g). The standard enthalpy of this reaction is –1418 kJ. What is the standard enthalpy of formation of nitromethane in kJ/mol?

a) -1.13E2
b) -1418
c) -709
d) -354

Answer 1

The standard enthalpy of formation for nitromethane is –709 kJ/mol, which is found by dividing the standard enthalpy of the combustion reaction (–1418 kJ) by the number of moles of nitromethane (2 moles) involved in the reaction.

Step-by-step explanation:

The combustion reaction of nitromethane fuel is 2 CH₃NO₂(l) + 3/2 O₂(g) → 2 CO₂(g) + 3 H₂O(l) + N₂(g), and the standard enthalpy (ΔH°) is –1418 kJ for the reaction as it stands, which involves the combustion of 2 moles of nitromethane. To find the standard enthalpy of formation for nitromethane (ΔH°f), this value must be divided by the number of moles of nitromethane that react, since ΔH°f always refers to 1 mole of the substance. Therefore, the standard enthalpy of formation for nitromethane is –1418 kJ / 2 moles = –709 kJ/mol.