Chapter 5, Problem 80E

Ethanol, ${\text{C}}_2{\text{H}}_5\text{OH}$, is used as a fuel for motor vehicles, particularly in Brazil.

(a) Write the balanced equation for the combustion of ethanol to ${\text{CO}}_2\left(g\right)$ and ${\text{H}}_2\text{O}\left(g\right)$, and, using the data in Appendix G, calculate the enthalpy of combustion of 1 mole of ethanol.

(b) The density of ethanol is 0.7893 g/mL. Calculate the enthalpy of combustion of exactly 1 L of ethanol.

(c) Assuming that an automobile’s mileage is directly proportional to the heat of combustion of the fuel, calculate how much farther an automobile could be expected to travel on 1 L of gasoline than on 1 L of ethanol. Assume that gasoline has the heat of combustion and the density of n—octane, ${\text{C}}_8{\text{H}}_{18}\left(\Delta H_{\text{f}}^{°}=-208.4\text{kJ/mol; density}=0.7025\text{g/mL}\right)$.