What is the standard free energy of formation for an element in its standard state (ΔGf)?

The standard free energy of formation, ΔGf, for an element in its standard state is defined as zero. This is based on the convention used in thermodynamics where the formation of an element from itself is essentially a reference point.

In practical terms, when we talk about the formation of an element in its standard state, we are referring to a process that does not require any energy change; it is essentially a definition rather than a reaction. Therefore, the standard free energy of formation for elements like oxygen, hydrogen, carbon, and others in their most stable forms (e.g., O2(g), H2(g), C(s, graphite)) is set to zero. This allows us to calculate the standard free energies of formation for compounds relative to these elements.

This convention provides a consistent basis for determining the thermodynamic stability of substances, where positive or negative values of ΔGf for compounds indicate their stability compared to the elemental forms. Elements in their standard state serve as a baseline reference for all other compounds.