Chapter 17 - 2. Gases are formed from either solids or...

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Spontaneity Spontaneous does not mean fast. Non-spontaneous does not mean impossible. If a process is spontaneous, the reverse process is non-spontaneous. http://mooni.fccj.org/~ethall/2046/ch20/spontaneous/spontan.htm 2
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Spontaneity and Disorder In spontaneous processes, systems go towards disorder. 3
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Entropy (S) Proportional to disorder in the system. Entropy (S) is a state function. ΔS = (q rev )/T Entropy increases in a spontaneous process. To predict increase/decrease in entropy figure out increase/decrease in disorder. Entropy changes in phase changes. ΔS 0 surr = -ΔH 0 sys T ΔS 0 = Σν p S 0 p - Σν r S 0 r Second law of thermodynamics: All spontaneous processes produce an increase in the entropy of the universe. ΔS univ = ΔS sys + ΔS surr > 0 Third law of thermodynamics: Entropy of a pure perfect crystal at 0 K is zero. 4
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Spontaneity: Criteria Increase in entropy: 1. Pure liquids or liquid solutions are formed from solids.
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Unformatted text preview: 2. Gases are formed from either solids or liquids. 3. Number of gas molecules increased as a result of a chemical reaction. 4. Temperature of a substance increases. Favorable Unfavorable H < 0 H > 0 S univ > 0 S univ < 0 5 Gibbs free energy (G) G = H -TS G = H TS for processes at constant temperature. Spontaneity: Additional crieteria G < 0 spontaneous G > 0 non-spontaneous G = 0 equilibrium Understand Table 17.1 G = H TS G = H TS (for ideal gas) G = p G p- r G r Favorable Unfavorable H < 0 H > 0 S univ > 0 S univ < 0 6 Free energy change and equilibrium G = G + RT lnQ G = G + RT lnK eq Direction of spontaneous change is the direction in which free energy decreases. 7...
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Chapter 17 - 2. Gases are formed from either solids or...

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