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Why is the Standard enthalpy of formation of O2 and other reference forms of element zero?

Well, from what I know bonding releases energy.

And does anybody know a source for finding the reference form of element at standardconditions?

physical-chemistry thermodynamics reaction enthalpy

edited Oct 28 at 1:00Philipp6,538 2 11 44

asked Oct 27 at 23:38user1.618250 8

1 Answer

It is purely a matter of definition. A standard enthalpy of formation describes the change in enthalpyduring the formation of 1 mol of a target compound by reacting the (pure) elements it consists of,whereby each element is expected to be in its most stable modification for the given temperature.Now take the case of oxygen as an example: At standard conditions is the most stablemodification of oxygen. That means at standard conditions the reactionH0

0 H

0

is defined in such a way that each of the elemental s are defined to be exactly the same state asan oxygen atom that is part of an , i.e. their enthalpy matches exactly that of

: . This gives you a reference point for which is otherwisenearly impossible to measure much as the Standard Hydrogen Electrode is used to set up areference system for the electrode potential.

0

H0

0

H0

0 H

0

0

A table showing some standard enthalpies of formation can be found . There it is also indicatedwhich phases are used as reference form.

here

edited Oct 28 at 10:15 answered Oct 28 at 0:13Philipp6,538 2 11 44