A new fuel, which has a molar mass of 112 g/mol and a density of 0.712 g/ml, is
ID: 788405 • Letter: A
Question
A new fuel, which has a molar mass of 112 g/mol and a density of 0.712 g/ml, is used in an automobile test run. The delta H of combustion for the fuel is -5.55x10^3 kJ/mol. The automobile has a 20.6 gal fuel tank. The energy delivered by the combustion of the fuel is 5.62 x 10^4 kJ/h at 60.0 mph.
What is the cruising range (in miles) of the automobile on a full tank, assuming all the energy is transferred to the wheels?
If the actual cruising range is 732 km, what is the efficiency of the engine?
Please show all work.
Explanation / Answer
20.6 gal = 78 litres
density = 0.712 g/ml
hence
total mass = 0.712*78000 = 55536 grams
no of moles = 55536/112 = 495.86 moles
hence
delta H = 5.55 x 10^3 * 495.86 = 2752007.14 kJ
power = 56200 kJ/hour
hence
net time = 2752007.14/56200 = 48.96 hours
velocity = 60 mph
hence
range = 48.96*60 = 2938 miles is the range
actual range = 732 km = 455 miles
time = 455/60 = 7.58 hours
power delivered = 2752007.14/7.58 = 363061.63 kJ/hr
hence efficiency = 56200/363061.63 *100 = 15.48 percent
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