Question

The heat of combustion of heptane and isooctane are -4501 kJ/mol and -5100 kJ/mol, respectively. Isooctane (2,2,4-trimethylpentane, pronounced iso-octane) is a pretty good model for the complex mixture of hydrocarbons that is gasoline. The density of these two liquids (essentially the same for all liquid hydrocarbons) is 0.7 g/mL (kg/dm3). What is the heat of combustion of one gallon of the two liquids? Are they essentially the same or quite different? Why? a. b. The U.S. Congress (our representatives) mandated that all gasoline sold in the U.S. contain a significant quantity of biomass-derived ethanol. Calculate the heat derived from combustion of a gallon of ethanol. Ethanol has a liquid density of 0.789 g/mL anda heat of formation of-276t 2 kJ mol1. Assume that you start with liquid ethanol and make gaseous products (what would be alternative assumptions?) Compare the heat of combustion of a gallon of ethanol to that of a gallon of isooctane ("gasoline). Do you think you can drive a car as far on a gallon of ethanol as on a gallon of isooctane? Nobel Laureate George Olah has written extensively about using methanol instead of ethanol, and DuPont and BP and others are advocating for bio-derived butanol as a better fuel than ethanol. Without calculating anything -just looking at the molecules and the products of combustion and trying to see a pattern - can you guess what the order of energy density is for the four molecules isooctane, ethanol, methanol, and butanol. Energy density is the heat of combustion per gallon. c. d.

Answer 1

200 2g Loo 10 Y 24 K3

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