Gasoline is composed primarily ofhydrocarbons with eight carbon atoms. These hyd

Question

Gasoline is composed primarily ofhydrocarbons with eight carbon atoms. These hydrocarbons are calledoctanes. One of the cleanest burning octanes is a compound called2,3,4-trimethylpentane. The complete combustion of 1mol of this compound to CO2(g) and water liquid leads to !H° =-5461 kJ. Write a balanced equation for the combustion of 1 mole ofC8H18(l). Write a balanced equation for the formationof C8H18 from its elements. By using the information in thisproblem, calculate the heat of formation for2,3,4-trimethdylpentane.

Explanation / Answer

The combustion reaction of theC8H18 is - C8H18 (l) + 25/2O2 (g) -----------> 8 CO2 (g) + 9H2O(l)           H0 = - 5461 kJ From the standard enthalpy of formation values, H0 (O2,g) = 0 kJ,H0 (CO2,g) = -393.5 kJ/mol,H0 (H2O,l) = -286 kJ/mol Therefore -                  H0 = H0 (products) -H0 (reactants)            - 5461 kJ = 8*-393.5 + 9*-286 kJ -H0 ( C8H18 )         H0 ( C8H18 )= -5722 kJ + 5461 kJ                                = -261 kJ The formation of C8H18 from itselements,     8 C (s) + 9 H2(g)   -------------> C8H18 (l)

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