Problem: Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4-trimethylpentane, which has the structural formula shown.The complete combustion of one mole of this compound to CO2(g) and H2O(g) leads to ΔH˚ = –5064.9 kJ/mol{ m kJ/mol}. By using the information in this problem and data given below, calculate ΔH˚f for 2,3,4-trimethylpentane.

FREE Expert Solution

C8H18(l) + 25/2 O2(g) → 8 CO2(g) and 9 H2O(g)


ΔH°rxn=ΔH°f, prod-ΔH°f, react


Note that we need to multiply each ΔH˚f by the stoichiometric coefficient since ΔH˚f is in kJ/mol. 

Also, note that ΔH˚f for elements in their standard state is 0.

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Problem Details

Gasoline is composed primarily of hydrocarbons, including many with eight carbon atoms, called octanes. One of the cleanest-burning octanes is a compound called 2,3,4-trimethylpentane, which has the structural formula shown.

The complete combustion of one mole of this compound to CO2(g) and H2O(g) leads to ΔH˚ = –5064.9 kJ/mol. By using the information in this problem and data given below, calculate ΔH˚f for 2,3,4-trimethylpentane.

Table of the standard enthalpies of formation at 298 K for various substances.


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