Typical hydrocarbon fuels (e.g., 2,2,4-trimethylpentane, a common component of gasoline) have very similar heats of combustion when

Question:

Typical hydrocarbon fuels (e.g., 2,2,4-trimethylpentane, a common component of gasoline) have very similar heats of combustion when calculated in kilocalories per gram.

(a) Calculate heats of combustion per gram for several representative hydrocarbons in Table 3-7.

(b) Make the same calculation for ethanol (Table 3-7).

(c) In evaluating the feasibility of “gasohol” (90% gasoline and 10% ethanol) as a motor fuel, it has been estimated that an automobile running on pure ethanol would get approximately 40% fewer miles per gallon than would an identical automobile running on standard gasoline. Is this estimate consistent with the results in (a) and (b)? What can you say in general about the fuel capabilities of oxygen-containing molecules relative to hydrocarbons?

Heats of Combustion [kcal mol- (kJ mol-1), Normalized to 25°C] of Various Organic Compounds Table 3-7 Compound (state) Name comb CH4 (gas) Methane -212.8 (-890.4) C,H, (gas) Ethane - 372.8 (-1559.8) CH,CH,CH3 (gas) Propane - 530.6 (-2220.0) CH3(CH2),CH3 (gas) Butane -687.4 (-2876.1) (CH3)3CH (gas) 2-Methylpropane -685.4 (-2867.7) CH3(CH,),CH, (gas) Pentane