Chapter 20 - Second Law of Thermodynamics All real processes occur ...

Chapter 20 - Second Law of Thermodynamics All real processes occur spontaneously in the direction that increases the entropy of the universe increases Suniverse = Ssystem + Ssurroundings > 0 - Third Law of Thermodynamics A perfect crystal has 0 entropy at absolute 0 (0 K) - Definition of the Gibbs Free Energy Gibbs Free Energy: determines the spontaneity of a process and the useful available energy from it - Using Free Energies to predict direction in chemical reactions < 0 spontaneous > 0 non-spontaneous = 0 at equilibrium - Relation of Gibbs Free Energy to maximum work = Wmax ; Work is done by a system during a spontaneous reaction; constant T and P = Wmin ; Work is done on a system during a non-spontaneous reaction; constant T and P - Relation of Gibbs Free Energy to equilibria constants RTlnQ - RTlnK - Temperature dependence of Gibbs Free Energy/relation to enthalpy and entropy Temperature independent Cases; when and have opposite signs 1. Reaction is spontaneous at all temperatures H < 0 and > 0; this makes -T negative, H is also negative; G is negative = spontaneous reaction 2. Reaction is non-spontaneous at all temperatures H > 0 and < 0; this makes -T positive, H is also positive; G is positive = spontaneous reaction Temperature Dependent Cases; when and have same signs 3. Reaction is spontaneous as the temperature increase: 0 and S > 0; only spontaneous at higher temperatures becomes negative and is negative 4. Reaction is spontaneous as the temperature decrease: 0 and S < 0; only spontaneous at lower temperatures becomes smaller than and is negative - Change in Free Energy, enthalpy, entropy with phase changes (solid liquid gas) Entropy: Solid < Liquid < Gas Enthalpy: Solid < Liquid < Gas Free Energy: = Dependent on size of