From the values given for ΔH° and ΔS°, calculate ΔG° for each of the following reactions at 298 K. If the reaction is not spontaneous under standard conditions at 298 K, at what temperature (if any) would the reaction become spontaneous? (a) 2 PbS1s2 + 3 O21g2¡2 PbO1s2 + 2 SO21g2 ΔH ° = -844 kJ; ΔS° = -165 J>K