gracy
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substances in their elemental state have enthalpies of formation equal to zero,why?
so no reason or concept behind this?Bystander said:Convention. There has to be an agreed upon zero, and this is as good as any.
cseil said:It is not some sort of convention.
It is just that elements are not formed, they exist like they are. That's it.
You don't form an element, element just exists.
You take one mole of O2 and turn it into one mole of O2.cseil said:How do you form O2 from its constituent elements if the costituent element at the most stable form is O2?
Bystander said:You take one mole of O2 and turn it into one mole of O2.
cseil said:I am sorry but isn't standard enthalpy of formation defined as the change of enthalpy that comes from the formation of 1 mol of the compound from its elements at the most stable state at 1 atm?
Certainly --- and ΔH for such a process is zero. However, what would I accomplish by breaking the bond in the first place? The mole of O2 doesn't need its bonds broken before I use it in whatever process I have in mind --- it's the zero point from which all measurements are made.cseil said:But don't you obtain the same energy again when the two bonds are formed again?