The heat of combustion of hydrocarbon is very useful source of heat and power, considering the combustion reaction given below. CH4(g) +O2(g) →CO2(o) + 2H2O △H for the reaction is:
Correct answer: A. △H = 213 kcal/mole
- A. △H = 213 kcal/mole
- B. △H = 231 kcal/mole
- C. △H = 426 kcal/mole
- D. △H = 312 kcal/mole
Explanation
The enthalpy of combustion of methane (CH4) is -890 kJ/mol. To convert this to kilocalories, use the conversion factor 1 kJ = 0.239 kcal. Therefore, -890 kJ/mol × 0.239 kcal/kJ = -212.715 kcal/mol, which rounds to approximately -213 kcal/mol. This makes Option A correct. The other options provide values that are not consistent with this conversion and the known enthalpy of combustion for methane.
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Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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