Question

A 1.738 g sample of a component of the light petroleum distillate called naphtha is found to yield 5.327 g CO2(g) and 2.544 g H2O(l) on complete combustion.

This particular compound is also found to be an alkane with one methyl group attached to a longer carbon chain and to have a molecular formula twice its empirical formula.

The compound also has the following properties:

melting point of −154 ∘C ,

boiling point of 60.3 ∘C ,

density of 0.6532 g/mL at 20 ∘C ,

specific heat of 2.25 J/(g⋅∘C) , and

ΔH∘f=−204.6kJ/mol .

Part C

Calculate the enthalpy of combustion, ΔH∘comb, for C6H14. You'll first need to determine the balanced chemical equation for the combustion of C6H14.

Express your answer to four significant figures and include the appropriate units.

Answer 1

ΔHcomb = -3849 kJ/mol

Step-by-step explanation:

For the alkane C₆H₁₄ the balance reaction of combustion is:

C₆H₁₄+ ¹⁹/₂ O₂(g) → 6CO₂(g) + 7H₂O(g)

It is possible to obtain ΔHcomb for this reaction from the standard enthalpies of formation using:

ΔHcomb = ΔH°products - ΔH°reactants.

For the combustion of the alkane C₆H₁₄:

ΔHcomb = 6ΔH°CO₂ + 7ΔH°H₂O - (ΔH°C₆H₁₄ + ¹⁹/₂ΔH°O₂)

Where:

ΔH°CO₂: -393,5 kJ/mol

ΔH°H₂O: -241,8 kJ/mol

ΔH°C₆H₁₄: -204,6 kJ/mol

ΔH°O₂: 0 kJ/mol

Replacing:

ΔHcomb = 6×-393,5 kJ/mol + 7×-241,8 kJ/mol - (-204,6 kJ/mol + ¹⁹/₂×0 kJ/mol)

ΔHcomb = -3849 kJ/mol

I hope it helps!