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Topic: enthalpy of heat/of formation question  (Read 4239 times)

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Offline XxslbabesxX

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enthalpy of heat/of formation question
« on: December 12, 2005, 12:01:43 AM »
What is the difference between ?H (enthalpy of heat) and ?Hf? (standard enthalpy of formation)? This is completely boggling me. To me, it seems like they are the same thing. If you have a reaction where the products are in their standard state would it mean that standard enthalpy of formation is the same as its enthalpy of heat ?

Offline Mr. Raru

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Re:enthalpy of heat/of formation question
« Reply #1 on: December 12, 2005, 09:19:41 PM »
standard enthalpy of formation's reactants are all elements, and not compounds
enthalpy of heat is the change for a reaction usually calculated with Hess's law or with the enthalpy of formation of reactants and the products.

Offline Donaldson Tan

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Re:enthalpy of heat/of formation question
« Reply #2 on: December 18, 2005, 12:28:48 PM »
enthalpy of heat refers to the amount of heat released by a chemical reaction at isobaric and isothermal condition at a specific pressure and temperature.

?Hf? refers to the enthalpy of heat for a specific reaction - the chemical reaction whereby a mole of a particular substance is formed from its elements at their natural state at standard conditions - 1atm and 298K.
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