Lec-14-Chap18-2-Complete

Lec-14-Chap18-2-Complete - Lec-14-Chap18-2-Complete...

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Lec-14-Chap18-2-Complete 10/9/2009 Directionality of Chemical Reactions Gibbs free energy. Calculations 1 Lec-14: Thermodynamics: Directionality of Chemical Reactions. Gibbs Free Energy Chapter 18 1 Since entropy measures , and increases with the number of microscopic states of the system , we can say that the disordered state has a higher entropy than the ordered one. Entropy is a measure of the number of microscopic states associated with the macroscopic state. Molecular Interpretation of the Entropy Calculate Δ for the following reactions:                       2 2 22 1 Ca s O g 2 1 Hg 2 11 Ng CaO s NO g 2 a b c Og 2 2     00 0 i 0 r 0 in products n reactant eaction 0 reac s tion CD PP P AB RR R aS bS S cS d S S S S     C+ D+ A+ B+ ab cd
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Lec-14-Chap18-2-Complete 10/9/2009 Directionality of Chemical Reactions Gibbs free energy. Calculations 2 Molecular Interpretation of the Entropy                     2 2 a J 1 CaO s CaO s J 39.748 K mol 04.241 K m 1 Ca s O g 2 1 Ca s O g 2 J 1 J 41.42 205.138 K mol 2 K mol ol S S S S S S             There is a substantial decrease in entropy because oxygen is converted from a form O 2 (g) in which there is considerable disorder to a form CaO(s) in which the atoms are well localized at crystal lattice points. 3 Molecular Interpretation of the Entropy               2 2 Hg J 11 1 b J 49.258 K mo 4.60 K mol l 2 1 2 1J 130.684 2 K mol S S S S S     Entropy increases because the H atoms are dissociated from one another, and there are more microscopic states available to them than when they are linked, as in H 2 . 4
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Lec-14-Chap18-2-Complete 10/9/2009 Directionality of Chemical Reactions Gibbs free energy. Calculations 3 Molecular Interpretation of the Entropy The entropy change is small, since the same number of moles are involved on the reactant and product sides. Furthermore the molecular structures are very similar.                     22 11 N g O g N g O g 1 J 1 J 191.61 205.138 2 K mol 2 K mol NO g NO g J 210.45 K mol c J 12.076 K mol S S S S S S       5 6 What is the sign of the standard entropy change in the reaction       32 MgCO s MgO s ?
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Lec-14-Chap18-2-Complete - Lec-14-Chap18-2-Complete...

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