Use the following definitions to answer the questions below. Energy density: the

Question

Use the following definitions to answer the questions below.

Energy density: the quantity of energy released per unit volume of fuel burned.

Fuel value: the quantity of energy released per unit mass of fuel burned.

Equal volumes of CH4 (g) and H2(g) burn.

CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g) Hrxn = 802.3kJ

2 H2 (g) + O2 (g) 2 H2O (g) Hrxn = 483.6kJ

Which fuel has the greatest energy density? (Anwer should come out to be: CH4 (g) (802.3 kJ/mol) compared to H2(g) (241.8 kJ/mol))

Which fuel has the greater fuel value?  (Anwer should come out to be: Hydrogen has the highest fuel value: CH4 (g) fuel value = 50.01 kJ/g;   H2 (g) fuel value = 119.9 kJ/g)

You can assume that the fuels are combusted under the same conditions and that the gases behave ideally.

Explanation / Answer

1) Energy density = CH4has greatest energy density. As per defination, energy released per unit volume menas there is only one methane molecule therefore energy density is 802.3 / 1 = 802.3 KJ.

Hydrogen is less energy density becouse there are two moles of hydrogens therefore energy density = 483.6 / 2 = 241.8 KJ.

2) Fuel value = Defination is the energy releases per unit MASS. Molar Mass of one mole of methane is 16. therefore fuel value = 802.3 / 16 = 50.1 KJ. And Molar mass of two moles of H2 to be 4. therefore Fuel value = 483.6 / 4 = 120.9 . Therefore Hydrogen has highest fuel value.

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