Many power plants produce energy by burning carbon-based fuels, which also produ

Question

Many power plants produce energy by burning carbon-based fuels, which also produces carbon dioxide Carbon dioxide is a greenhouse gas, so over-production can have negative effects on the environment Use enthalpy of formation data to calculate the number of moles of CO2(g) produced per megajoule of heat released from the combustion of each fuel under standard conditions (1 atm and 25°C). (a) coal, C(s, graphite) (b) natural gas, CH4(g); Number Number mol MJ mol MJ- (c) propane, C3H8(g) (d) octane, C8H18() (-250.1 kJ-mol-1). Number Number mol MJ mol MJ1

Explanation / Answer

Part A : mols of CO2/M.J-1

(a) Coal (graphite, s)

C(grahite,s) + O2(g) ---> CO2(g)

dHfo = dHfo(products) + dHfo(reactants)

        = -393.509 kJ = -0.3935 MJ

moles of CO2 produced = 1/-0.3935 = -2.54 mol/MJ-1

(b) natural gas, CH4(g)

CH4(g) + O2(g) ---> CO2(g) + 2H2O(g)

dHfo = dHfo(products) + dHfo(reactants)

        = (-393.509 + 2 x -241.818) - (-74.9)

        = -802.245 kJ = -0.802 MJ

moles of CO2 produced = 1/-0.802 = -1.25 mol/MJ-1

(c) Propane, C3H8(g)

C3H8(g) + 5O2(g) ---> 3CO2(g) + 4H2O(g)

dHfo = dHfo(products) + dHfo(reactants)

        = (3 x -393.509 + 4 x -241.818) - (-104.6 + 5 x 0)

        = -2043.20 kJ = -2.043 MJ

moles of CO2 produced = 3/-2.043 = -1.45 mol/MJ-1

(d) Octane, C8H18(g)

2C8H18(g) + 25O2(g) ---> 16CO2(g) + 18H2O(g)

dHfo = dHfo(products) + dHfo(reactants)

        = (16 x -393.509 + 18 x -241.818) - (2 x -250.1)

        = -10148.67 kJ = -10.15 MJ

moles of CO2 produced = 16/-10.15 = -1.58 mol/MJ-1

Part B. The correct reaction for the formation of CaO(s) would be,

Ca(s) + 1/2O2 ---> CaO(s)

the heat of formation for this reaction equals the standard heat of formation for CaO(s) data.

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