Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fue

Question

Hydrogen and methanol have both been proposed as alternatives to hydrocarbon fuels.

a) Write balanced reactions for the complete combustion of hydrogen.

b)Use standard enthalpies of formation to calculate the amount of heat released per kilogram of the fuel.Express your answer using four significant figures.(kJ/kg)

c)Write balanced reactions for the complete combustion of methanol.Express your answer as a chemical equation. Identify all of the phases in your answer.

d)Use standard enthalpies of formation to calculate the amount of heat released per kilogram of the fuel.Express your answer using four significant figures.(kJ/kg)

e)Which fuel contains the most energy in the least mass? Hydrogen or Methanol

f)How does the energy of these fuels compare to that of octane (C8H18)?Express your answer using four significant figures. (kJ/kg)

Explanation / Answer

a) The balanced equation for combustion of H2 is

2H2 + O2 2H2O

b)

H2 + 1/2 O2 H2O

H° = ( × Hf°) (products) - ( × Hf°) (reactants), is respective stoichiometric coefficient,

Hreaction = ( -285.8) -[(1/2*0)+(1*0)] - = -285.8 kJ/mol

Per 2g of it is -285.8 kJ

So, heat released per kilogram of H2 = -142900 kJ/kg

c) balanced equation for the complete combustion of methanol

2CH3OH(g) + 3O2(g) 2CO2(g) + 4H2O(l)

d)

2CH3OH(g) + 3O2(g) 2CO2(g) + 4H2O(l)

CH3OH(g) + 3/2 O2(g) CO2(g) + 2H2O(l)

Hreaction = [(-393.5)+(2*-285.8)] - [(-238.6)+(3/2*0)]= -965.1+238.6 =-726.5 kJ/mol

32.04 g of methanol gives -726.5 kJ

Heat released per kilogram of methanol = -22674.7815 kJ

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