Here we want to compare ethanol (C₂H₅OH) and gasoline as fuels. We will use isooctane (C₈H₁₈) as a substitute for gasoline. (Isooctane is one of the many hydrocarbons in gasoline, and its enthalpy of combustion will approximate the energy obtained when gasoline burns. See Study Question 22.)
(a) Calculate Δ_rH° for the combustion of 1.00 kg each of liquid ethanol and liquid isooctane. Which fuel releases more energy per kilogram?
[Δ_fH° = −259.3 kJ/mol for liquid isooctane at 298 K.] (Assume H₂O(ℓ) is one product of combustion.)
(b) Compare the two fuels on the basis of the release of CO₂, a common greenhouse gas. Which fuel produces more CO₂ per kilogram?
(c) On the basis of this simple comparison and neglecting the energy costs involved in producing 1.00 kg each of ethanol and isooctane, which is the better fuel in terms of energy production and greenhouse gases?

Data given in Question 22

The enthalpy of combustion of isooctane (C₈H₁₈), one of the many hydrocarbons in gasoline, is 5.45 × 10³ kJ/mol. Calculate the enthalpy change per gram of isooctane and per liter of isooctane (d = 0.688 g/mL).

Transcribed Image Text:

isooctane C₂H 18