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# ch10_pdf - Chapter 10 Thermodynamics The Second Law Entropy...

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Chapter 10 Thermodynamics: The Second Law Entropy Spontaneity of Reactions Gibbs Free Energy

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Two exothermic reactions: N 2 H 4 (l) + 2H 2 O(l) Æ N 2 (g) + 4H 2 O(g) H rxn o = -642 kJ/mole 2H 2 S(g) + SO 2 (g) Æ 3S(s) + 2H 2 O(l) H rxn o = -233 kJ/mole Only the first reaction is spontaneous. Why? ENTROPY
Entropy is the level of disorder in a system. Which system is more disordered?

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Second Law: The entropy of a system increases in any spontaneous process, and the natural progression is from low to high entropy. Entropy: S units of J/K
Hot Cool

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Liquid Solid Which has more disorder?

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Increasing disorder (increasing entropy): • Molecules that are farther apart • Substances whose volume increases • Molecules that are mixed up (mixtures) How to increase entropy of a system? Expand it, heat it, mix it, break up intermolecular forces.
Increasing entropy; increasing disorder

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Standard Molar Entropy of Water at Various Temperatures
Absolute Entropies at 298 K for a Few Common Substances

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Calculation of Entropy S = q/T or H/T or n C ln T 2 /T 1 or n R ln V 2 /V 1 or n R ln P 1 /P 2 (C is heat capacity)
1000. J of energy is added as heat at 25 o C. What is the increase in entropy of the water?

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ch10_pdf - Chapter 10 Thermodynamics The Second Law Entropy...

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