Natural gas is primarily composed of methane (CH4), while coal can be modeled as

Question

Natural gas is primarily composed of methane (CH4), while coal can be modeled as eicosane (C20H42). Methane has a heat of combustion of 55.6 MJ/kg, and its molecular weight is 16 g/mol. Correspondingly, eicosane has a heat of combustion of 47.2 MJ/kg, and its molecular weight is 282 g/mol. If you generated the same total amount of heat with each fuel, which would produce more CO2 emissions? By how much? (Hint: Remember that hydrocarbon consumption produces one CO2 molecule for each carbon atom in the fuel.)

Explanation / Answer

CH4 + 2O2 --> C02 + 2H2O

1 mole CH4 (16g of CH4) releases 1 mole CO2..

therefore H = 55.6MJ/Kg x 0.016 Kg = 0.8896 MJ..

C20H42 + 61/2O2 --> 20CO2 + 21H2O

1 mole C20H42 (282g of C20H42) releases 20 mole CO2..

therefore H = 47.2MJ/Kg x 0.282 Kg = 13.3104 MJ..

For producing same amount of energy as C20H42 (13.3104 MJ), [13.3104/0.8896] = 14.96 moles of CH4 is to be used..

14.96 moles of CH4 gives releases 14.96 moles of CO2...

1 mole C20H42 (282g of C20H42) releases 20 mole CO2..

And both produce same amount of energy, i.e 13.3104 MJ energy..

C20H42 gives more CO2 emissions..

By [20/14.96] = 1.33 times..

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