Motor vehicle environmental effects are judged on the grams of carbon dioxide emitted per kilometre of travel.
The combustion equations for bioethanol and the alkane ethane and the energy liberated are:
C2H5OH + 3O2 --> 2CO2 + 3H2O, delta H = -1371 kJ mol-1
and
C2H6 + 7/2O2 --> 2CO2 + 3H2O, delta H = -1560 kJ mol-1
Bearing in mind that the car is driven by the energy liberated, state which fuel would be more environmentally friendly per mol on the basis of these results, giving your reason.
There is however, another factor to be considered. Discuss this and state whether or not your initial conclusion should be altered.