In considering the energy supply for an automobile, the energy per unit mass of
ID: 1897216 • Letter: I
Question
In considering the energy supply for an automobile, the energy per unit mass of the energy source is an important parameter. The "heat of combustion" or stored energy per mass is quite similar for gasoline, ethanol, diesel fuel, cooking oil, methane, and propane. For a broader perspective, compare the energy per mass in joules per kilogram for gasoline, lead-acid batteries, hydrogen, and hay by stating the factor of increase between each one and the next. Hydrogen has "heat of combustion" 142 MJ/kg. For wood, hay, and dry vegetable matter in general, this parameter is 17 MJ/kg. A fully charged 16.0 kg lead-acid battery can deliver power 1050 W for 1.0 hr. (For comparison, the "heat of combustion" of gasoline is about 44 MJ/kg.)
Explanation / Answer
MJ means mega joule .
Gasoline 44 MJ/kg
hydrogen 142 MJ/Kg
hay 17MJ/KG
1 hr =3600 sec
lead acid can deliver 1050 w x 3600 sec =3780000 joule per 16kg
it 3.78 MJ/16 kg or
0.23625 MJ/Kg
so lead acid delivers the least amount of energy per kg
hay is larger than lead acid battery (17>0.23625)
gasoline is larger than hay (44> 17)
hydrogen is larger than gasoline ( 142>42) it due to the very low density of hydrogen .
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