5.2 Chapter 19 Entropy and Free Energy (6 per page)

5.2 Chapter 19 Entropy and Free Energy (6 per page) - Ch....

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Spontaneous Change 19-1 Spontaneity: The Meaning of Spontaneous Change 19-2 The Concept of Entropy 19-3 Evaluating Entropy and Entropy Changes 19-4 Criteria for Spontaneous Change: The Second Law of Thermodynamics 19-5 Standard Free Energy Change, Δ G ° 19-6 Free Energy Change and Equilibrium 19-7 Δ G ° and K eq as Functions of Temperature • There is a ‘natural’ direction for change in chemical processes. • The natural direction is the one in which the system will proceed if ‘left to its own devices’ – i.e. not subject to external influence. • We call these Spontaneous ; changes that proceed without apparent external influence, force, cause or treatment. 19-1 Spontaneity: The Meaning of Spontaneous Change The direction of spontaneous change generally depends on temperature N 2 (g) + O 2 (g) 2 NO(g) At Equilibrium: Reactants are favoured at low temperatures, but products are favoured at high temperatures 2NO(g) + O 2 (g) 2 NO 2 (g) At Equilibrium: Products are favoured at low temperatures, but Reactants are favoured at high temperatures A Plausible Criteria for Spontaneous Processes Potential energy decreases – spontaneous process are always ‘downhill’ (maybe?) For chemical systems the internal energy, U , is analogous to mechanical potential energy. Berthelot and Thomsen 1870’s. Spontaneous change occurs in the direction in which the enthalpy of a system decreases. Mainly true but there are many exceptions. A spectacular exception to this rule 19-2 The Concept of Entropy; S Entropy, S . A statistical description: – The greater the number of ways there are to arrange the microscopic particles among the energy levels in a particular system, the greater the entropy of the system. Δ
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5.2 Chapter 19 Entropy and Free Energy (6 per page) - Ch....

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