One mole of ethanol generates 1235.4 kJ of energy through combustion and one mol

Question

One mole of ethanol generates 1235.4 kJ of energy through combustion and one mole of octane generates 5074.1 kJ of energy through combustion. The molar masses and densities of these two fuels are given in the table below. Using the information given in the table, apply unit analysis to calculate the amount of energy produced by burning one gram of each of the two fuels, the amount of energy produced by burning one liter of each of the two fuels, and the moles of each fuel per liter of fuel. Choose the best numerical answer for (a) through (e) to complete the table.

Type of Fuel Ethanol Octane Molar Mass (g/mol) 46.07 g/mol 114.22 g/mol Density (g/mL) 0.785 g/mL 0.699 g/mL Energy produced per mole of fuel (kJ/mol) 1235.4 kJ/mol 5074.1 kJ/mol Energy produced per gram of fuel (kJ/g) (a) (b) Energy produced per liter of fuel (kJ/L) (c) (d) Moles of fuel per liter (mol/L) (e) (f)

Explanation / Answer

One gram ethanol gives = dH per mole /mol mass = 1235.4/46.07 = 26.82 KJ

one gram octane gives = 5074.1/114.22 = 44.42 KJ

hence octane gives more energy per gram

one liter ethanol means 1000 x 0.785 gm = 785 gm

Energy = 785 x 26.82 = 21050 KJ

one liter octane means 1000 x 0.699 = 699 gm

energy per 1 liter = 44.2 x 699 = 30896 KJ

hence octane gives more energy per liter

moles of ethanol per liter = 785/46.07 = 17

moles of octane per liter = 699/114.22 = 6.12

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