Substance | CH₄(g) O₂(g) CO₂(g) H₂O(g)
ΔH° (kJ/mol) | -75 0 -390 -240
Natural gas consists primarily of CH₄, which is combusted according to the following chemical equation: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g). Based on the standard enthalpies of formation in the table above, which of the following expressions gives the approximate enthalpy change for the reaction?
a) ΔH°rxn = (–75 kJ/mol) – [(-390 kJ/mol) + 2(-240 kJ/mol)]
b) ΔH°rxn = (-75 kJ/mol) – [(-390 kJ/mol) + (-240 kJ/mol)]
