Standard Enthalpy Of Formation

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The standard enthalpy of formation of an element in its most stable state at 298 K and 1 atm is:

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By thermodynamic convention, the **Standard Enthalpy of Formation ($\Delta H_f^\circ$)** of a chemical element in its most stable physical state at $298 	ext{ K}$ and $1 	ext{ atm}$ pressure is **zero**.
- This provides a reference point for calculating enthalpies of compounds.
- Examples: $\Delta H_f^\circ[O_2(g)] = 0$, $\Delta H_f^\circ[C(graphite)] = 0$, $\Delta H_f^\circ[Fe(s)] = 0$.
- Unstable allotropes like $O_3$ or carbon diamond have non-zero enthalpies of formation.

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Standard Enthalpy Of Formation

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ΔH°f of elements in their most stable form at 298 K is:

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