High Octane Gasoline Gasoline is a complex mixture of hydrocarbons, including di

Question

High Octane Gasoline Gasoline is a complex mixture of hydrocarbons, including different isomers of octane. Gasoline is sold with a variety of octane ratings that are based on the comparison of the gasoline with the combustion properties of isooctane, a structural isomer of Cohs The structure of isooctane and another isomer of CalHs are shown in the figure below,along with their normal boiling points and heats of vaporization. Determine the vapor pressure of each isomer on a very hot summer day, 39.0°C

Explanation / Answer

For iso octane the antoine equation is given by

Log10(P) = 3.93679- 1257.84/(T -52.415)

Where Pressure is in bar and Temperature is in K

Substituting T = 39 oC = 312.15 K

subsituting T is above equation

Log10(P) = 3.93679- 1257.84/(312.15 -52.415)

P = 0.124167 bar = 93.132 torr

Now for tetramethyl butane

Log10(P) = 5.08335- 1724.764/(T -38.383)

Substituting T = 39 oC = 312.15 K

Log10(P) = 5.08335- 1724.764/(312.15 -38.383)

P = 0.06077 bar = 45.58 torr

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