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Thermodynamics and Spontaneity

Thermodynamics and Spontaneity. Spontaneous change : the direction of change that does not require work (outside assistance) to bring it about. Spontaneous chemical reactions often are exothermic: Are all exothermic reactions spontaneous (Bertholet C19)?.

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Thermodynamics and Spontaneity

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  1. Thermodynamics and Spontaneity Spontaneous change: the direction of change that does not require work (outside assistance) to bring it about Spontaneous chemical reactions often are exothermic: Are all exothermic reactions spontaneous (Bertholet C19)? Ice melting, water vapourisation, NaI dissolving in water are all spontaneous processes, yet are ENDOthermic. Accompanied by an increase in the “randomness” of the distribution of the particles. An increase in ENTROPY (S) 2nd LAW: Spontaneous changes in the universe are accompanied by an increase in disorder of the universe (cannot win, can only break even) Ssystem + Ssurroundings > 0

  2. 3rd LAW The entropy of a perfectly ordered crystalline substance is zero at 0 K (cannot break even) Sometimes enthalpy and entropy work together to favour a spontaneous change. What is their relative importance when they don’t? Use the Gibb’s Free Energy (G) devised by J.W. Gibbs. G is the maximum energy in a change that is free to do work G = H - T.S, therefore, for a change at a constant T G = H - T. S Spontaneous change in a system is accompanied by a negative free energy change

  3. Gibb’s Free Energy G = H - T. S At equilibrium, G is zero and Go = -RTlnK

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