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)

$\boxed{\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{rxn}}\mathbf{=}\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{f}\mathbf{,}\mathbf{ }\mathbf{prod}}\mathbf{-}\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{f}\mathbf{,}\mathbf{ }\mathbf{react}}}$

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.