What defines the standard Gibbs energy of formation (Δ_fG®)?

The standard Gibbs energy of formation (Δ_fG®) is specifically defined as the change in Gibbs free energy when one mole of a compound is formed from its constituent elements in their standard states. Standard conditions typically refer to a pressure of 1 bar and a specified temperature, usually 298.15 K.

This definition emphasizes the origin of the compound — indicating that we start with the pure elements (in their most stable forms) and form one mole of the desired compound. The standard Gibbs energy of formation is crucial for predicting the spontaneity of reactions and understanding thermodynamic stability.

The other options relate to different thermodynamic concepts. For instance, the energy change of a reaction under standard conditions does not specifically pertain to the formation of a single compound from its elements. The concept of maximum work done in a process and the energy associated with a change in temperature concern different aspects of thermodynamics that do not directly define Gibbs energy of formation.