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  PbS(s) + 3  O₂(g) → 2  PbO(s) + 2  SO₂(g) ΔH° = −844  kJ;  ΔS° = −165  J/K

Key Concepts

Gibbs Free Energy (ΔG)

Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. A negative ΔG indicates that a reaction is spontaneous under the given conditions.

Enthalpy (ΔH)

Enthalpy (ΔH) is a measure of the total heat content of a system. It reflects the energy required to break and form bonds during a chemical reaction. A negative ΔH value, as in the given reaction, indicates that the reaction is exothermic, meaning it releases heat to the surroundings, which can favor spontaneity.

Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. In thermodynamics, an increase in entropy is generally associated with the spontaneity of a process. A negative ΔS value, as provided in the question, suggests that the reaction leads to a decrease in disorder, which can hinder spontaneity unless compensated by a sufficiently negative ΔH at higher temperatures.