Enthalpy question

[Theiananator]

Does the heat of combustion of a compund = the heat of formation?

 

[bobsmith1492]

Hfg is the energy required to go from a saturated liquid to a saturated vapor... that's all we've used in thermo class.

Ok, I googled it; first link said the heat of formation is the energy produced or consumed in a reaction, so since combustion is reaction, it makes sense that the heat of combustion is the heat of formation for a combustion reaction.

 

[CycloWizard]

Heat of formation and heat of combustion are not the same. Heat of formation is the energy input necessary to form a given compound from its component elements (or, if a diatomic gas is a constituent, its natural molecular form such as O2). The heat of combustion is the energy of reaction when the compound is reacted with oxygen only.

 

[iwantanewcomputer]

no, i think it is opposite for specific reactions where the combustion is transforming the compound into it's natural states.
C +O2 -> CO2 heat of combustion is the heat of reaction, or enthalpy of CO2 - enthalpy of C -enthalpy of O2
heat of formation of CO2 is the same