Isooctane (2,2,4-trimethylpentane), one of the many hydrocarbons that make up gasoline, burns in air to give water and carbon dioxide. What?

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2017-09-24 7:57 pm

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Isooctane (2,2,4-trimethylpentane), one of the many hydrocarbons that make up gasoline, burns in air to give water and carbon dioxide. What is the enthalpy change if you burn 2.50 L of isooctane (d = 0.69 g/mL)?

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不用客氣

2017-09-24 8:39 pm

According to: http://webbook.nist.gov/cgi/cbook.cgi?ID=C540841&Mask=2
Heat of combustion of isooctane = -5461.3 kJ/mol

Mass of isooctane = (2.50 L) × (1000 mL/L) × (0.69 g/mL) = 1725 g
Molar mass of isooctane (C₈H₁₈) = (12.0×8 + 1.0×18) g/mol = 114.0 g/mol
No. of moles of isooctane burned = (1725 g) / (114.0 g/mol) = 15.13 mol

Enthalpy change for burning 2.5 L of isooctane = (-5461.3 kJ/mol) × (15.13 mol) = -82600 kJ
(The "-" sign indicates the energy is released to the surroundings.)

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