Delta G is the work so combustion of ethanol is C 2 H 5 OH + 3 O 2 ====== 2 CO 2

Question

Delta G is the work

so combustion of ethanol is

C2H5OH + 3 O2 ====== 2 CO2 + 3 H2O

Now apply Delta Gibss = Gibs products - Gibbs reactants

Gibbs product = 2 CO2 + 3 H2O = 2 * -394.4 + 3 * -228.6 = -1474.5 KJ / mol

Gibbs reactants = Ethanol + 3O2 = -174.8 + 3 *0 = -174.8

Delta gibbs = -1474.5 - (-174.8) = -1299.7 KJ / mol

molar mass of ethanol is 46

moles = 136/45 = 2.95 moles

maxium useful work is -1299.7 KJ / mol * 2.95 moles = - 3834.115 KJ

Combustion for Octane is

2 C8H18 + 25 O2 ====== 16 CO2 + 18 H2O

Gibbs products =   16* -394.4 + 18 * -228.6 = -10 425.2 KJ

Gibbs reactants = 2 * 17.3 + 0 = 34.6 KJ

Delta gibbs =  -10 425.2 KJ - 34.6 KJ = -10459.8 KJ

Since this is for 2 moles of octane we have to divide by 2

gibbs = -5229.9 KJ / mol, this is a lot of energy

Until this point octane has a higher energy making it a better fuel

To find the basis per gram just divide the values by the molar mass

Ethanol

-1299.7 KJ / mol * 1 / 46 = -28.25 KJ / gr

Octane

gibbs = -5229.9 KJ / mol * 1 / 114.2 = -45.79 KJ /gr

So from this values we can say that octane is a better fuel

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Explanation / Answer

A) Maximum Work ______kJ

B) Which is the better fuel?

i)The ethanol is a better fuel on a per gram basis, but the octane is better on a per mole basis.

ii)The octane is better fuel on both per gram and per mole basis

iii)The ethanol is a better fuel on both per gram and per mole basis.

iiii)The octane is a better fuel on a per gram basis, but the ethanol is better on a per mole basis.

(kI mol-1) 604.2 896.76 1320.3 Substance (kJ mo Substance CaO(s) Ca(OH)20) CaSO4(6) CaSO H2O1435.2 CaSO4 2H2O1795.7 C2(g) Fe(s) (kJ mol-) Substance K,SO4) -1316.4 N2(g) NH3(g NH4CI(s) NO(g) NO2(g) N2O(g) N2040g) Na() Na2CO -1048 NaHCO) 851.9 NaCI(s) NaOH(s) Na2SO4 1266.8 O2(g) PbO(s) 0 AgCI(s) Al(s) 0 16.7 203.9 +86.69 +51.84 109.7 0.00 1576.4 0 137.3 394.4 C() (graphite) CO(g) CO2(g) CHAg) CH,CI(g) CH3OH(D) CO(NH22(s)-197.2 CO(NH22la)-203.8 C2H2(g) 0 0 741.0 0 228.6 237.2 -95.27 79.91 689.9 392.5 0 +31.8 0 408.3 +103.6 50.79 58.6 166.2 +98.28 H20g) H2Og H,O(U) HCI(g) HNO3() H2SO4(U) HCH,02() Hg(l) Hg(g) K(s) KCI() 0 384.0 382 +209 +68.12 32.9 174.8 +17.3 CH6g CH,OHV) CgHis(l) Ca(s) CaCO3(s) CaCl2() 0 189.3 SO2(g SO3(g) 300.4 370.4 1128.8 750.2

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