Given reaction: C8H18(l) + 25/2 O2(g) → 8 CO2(g) + 9 H2O(g)
Part A:
Lewis Structures of the reaction:
Recall:
Average Bond Energies: found online or in textbooks
Reactants/Broken: Products/Formed:
• C–H = 410 kJ/mol • C=O = 732 kJ/mol
• C–C = 350 kJ/mol • O–H = 460 kJ/mol
• O=O = 498 kJ/mol
C8H18(l)+252O2(g)→8CO2(g)+9H2O(g)
Part A
Calculate ΔHrxn for the combustion of octane (C8H18), a component of gasoline, by using average bond energies. Express your answer using three significant figures.
ΔHrxn = _____ kJ/mol
Part B
Calculate ΔHrxn for the combustion of octane by using enthalpies of formation from Appendix IIB in the textbook. The standard enthalpy of formation of C8H18 is -250 kJ/mol.Express your answer using three significant figures.
ΔHrxn = _____ kJ/mol
Part C
What is the percent difference between the two results? Express your answer using two significant figures.
_____ %
Part D
Which result would you expect to be more accurate?
a) the value calculated from the heats of formation.
b) the value calculated from the average bond energies.
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