Answer to Question #115667 in General Chemistry for Nora

Question

What is the Delta Hf value for octane given that the complete combustion of mole of octane to produce carbon dioxide gas and steam releases 5074.248 kJ of enthalpy?

Answer 1

The standard enthalpies of formation of CO2 and H20 are given:

CO2(g)ΔHf= -393.5kJ/mol

H2O(l) ΔHf= -285.8kJ/mol

$C 8 H 1 8 + 12.5 O 2 → 8 C O 2 + 9 H 2 O$

$\delta Hf =Hf(r)- Hf(p)$

dHf= 5074.248-( (-393.5*8)+(-285.8*9)

dHf =10795.35kJ/mol