12-3-the-second-and-third-laws-of-thermodynamics_summary

The Second Law of Thermodynamics states that all spontaneous changes cause an increase in the entropy of the universe. Spontaneous processes result in an increase in entropy of the system, whereas nonspontaneous processes result in a decrease in entropy of the universe. The Third Law of Thermodynamics: the entropy of a pure, perfect crystalline substance at absolute zero (0 K) is zero. The Second Law of Thermodynamics can be used to predict the spontaneity of a process by calculating the entropy change of the universe (ΔSuniv). A positive ΔSuniv indicates a spontaneous process, while a negative ΔSuniv indicates a nonspontaneous process. The Third Law of Thermodynamics states that the entropy of a pure, perfect crystalline substance at absolute zero is zero. Standard entropies (S°) can be found for one mole of substance under standard conditions (1 bar and 298.15 K) and used to calculate the standard entropy change (ΔS°) for a process.