Final answer:
The Gibbs energy is a measure of the spontaneity or tendency for a reaction to occur. Standard Gibbs energies of formation can be used to calculate the Gibbs energy change for a reaction. A negative AG value indicates a spontaneous reaction, while a positive value indicates a nonspontaneous reaction.
Step-by-step explanation:
The question refers to the Gibbs energies at 25°C for various substances. The Gibbs energy is a measure of the spontaneity or tendency for a reaction to occur. In this case, the values given for Ag, Cl, AgCl, Br, and AgBr represent the standard Gibbs energies of formation, which is the change in free energy when 1 mole of a substance is formed from its elements in their standard states.
Standard Gibbs energies of formation can be used to calculate the Gibbs energy change for a reaction using the equation AG° = ΣAG(products) - ΣAG(reactants). If the calculated value of AG° is negative, the reaction is spontaneous, while a positive value indicates a nonspontaneous reaction.