(10 points) If all of the chemical energy in one drop of gasoline (which can be
ID: 784880 • Letter: #
Question
(10 points) If all of the chemical energy in one drop of gasoline (which can be assumed to consist of pure octane) is converted to lifting a tennis ball (57 g) against the gravitational field of the earth, how high up off the ground would the ball be? In other words, equate the potential energy of the tennis ball with the total chemical energy in the drop of gasoline. For this problem, the chemical energy in the gasoline can be taken to be equal to the enthalpy change in the reaction with oxygen to produce carbon dioxide and water (combustion 1 A typical drop is about 50 microliters, and you can probably nd any other information about octane that you need at www.nist.gov/chemistry (the so-called NIST Webbook").
Explanation / Answer
50 ul octane = 50 x 0.703 = 35.15 ugm ( 0.708 is density)
micromoles = 35.15/114.23 = 0.3077,
C8H18 + 12.5O2 --> 8CO2 + 9H2O
dH rxn = 9 dH H2O + 8 dH CO2 -dH C8H18
= 9(-241.8) + 8(-393.5) -(-208.4)
= -5115.8 KJ/mol
enegry released = 0.3077 x10^-6 x (5115.8) x1000 = 1.574 Joules
mgh = 1.574
0.057 x9.8 x h = 1.574
h = 2.818 meters
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