Given ΔH°, ΔS°, and T, determine spontaneity under standard conditions using ΔG° = ΔH° − TΔS°.

• A. If ΔG° > 0, the reaction is spontaneous at that T.
• B. If ΔG° < 0, the reaction is spontaneous at that T.
• C. If ΔG° < 0, the reaction is nonspontaneous.
• D. If ΔG° = 0, the reaction is spontaneous.

Answer: (B)

Spontaneity at a given temperature is determined by the sign of the Gibbs free energy change. Under standard conditions, ΔG° = ΔH° − TΔS°. If ΔG° is negative, the process can proceed without input, so it is spontaneous at that temperature. If ΔG° is positive, the process does not occur spontaneously, and if ΔG° is zero, the system is at equilibrium.

So, the statement that matches is: when ΔG° is negative, the reaction is spontaneous at that temperature. Positive ΔG° would mean nonspontaneous, and ΔG° = 0 corresponds to equilibrium, not spontaneity.