What reference state is used to report the standard Gibbs energies of formation of ions?

The standard Gibbs energy of formation of ions, particularly for the hydrogen ion in aqueous solution, is defined as zero. This reference state is pivotal in thermodynamics, allowing for a common baseline when calculating and comparing the standard Gibbs energies of formation for other species.

Setting the Gibbs energy of formation of the hydrogen ion to zero simplifies the calculation of standard Gibbs energies of formation for other ions and compounds. Essentially, it acts as a reference point, since all thermodynamic values are relative and must be set against a standard. The choice of hydrogen ion is conventional in aqueous chemistry, where it forms the basis for defining acidity and pH.

This is foundational in physical chemistry, particularly in electrochemistry and thermochemistry, as it helps in deriving potential values and reaction spontaneity based on Gibbs free energy. Therefore, establishing the hydrogen ion's Gibbs energy of formation as zero is critical for consistency and clarity in reporting and interpreting thermodynamic data.