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Enthalpy formation value for octane

Using the heat of combustion of octane C8H18 (l) -5470.5 and heat of formation table determine the enthalpy formation value for octane.

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First of all, let's balance the equation:

C8H18(l) + 25/2 O2 ------> 8 CO2 + 9 H2O -5470.5 kJ

Now, we need the other reactions that we can look up in the standard heat of formation table as you mentioned.

C(s) + O2(g) ----> CO2(g) -394 kJ

But to balance this with the first equation, we need to multiply it by 8. Therefore,

8 C(s) + 8 O2(g) ...

Solution Summary

This solution uses the heat of combustion of octane to determine its enthalpy formation value.