alleryStart learning →Burning 1.00 L of isooctane (density 0.692 g/mL, 114 g/mol, -5460 kJ/mol) produces how much heat?
AAbout 3.31 x 10^4 kJ
BAbout 5.46 x 10^3 kJ
CAbout 3.78 x 10^6 kJ
DAbout 8.99 x 10^2 kJ
Answer & Solution
Correct answer: A. About 3.31 x 10^4 kJ
1. Convert the volume: 1.00 L is 1.00 times ten cubed millilitres.
2. Convert to mass: 1000 mL times 0.692 g/mL gives 692 g of isooctane.
3. Convert to moles: 692 g divided by 114 g/mol gives 6.07 mol.
4. Apply the enthalpy of combustion: 6.07 mol times minus 5460 kJ per mole.
5. That product is about minus 3.31 times ten to the fourth kilojoules.
6. So burning 1.00 L of isooctane produces roughly 33,100 kJ of heat.
7. Skipping the density step and treating 1.00 L as 1 mol would give only 5460 kJ.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.3 Enthalpy_
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