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# ForExam4 - Exam#4 will cover Spontaneity and entropy...

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Exam #4 will cover: Spontaneity and entropy: - Boltzmann formula - entropy and disorder - entropy and heat - the Gibbs free energy at standard and non-standard conditions - T, p, C dependence of G - the Gibbs free energy and equilibrium Electrochemistry: - cell potential and the Gibbs free energy at standard and non-standard conditions, concentration effects - equilibrium constant and cell potential - electrolysis, batteries, fuel cells Equilibrium, Le Chatelier principle, acid/base/solubility concepts, thermochemistry and RedOx rxns are implicitly included

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react o prd o rxn S S S ) ( ) ( react H prd H H f o f o rxn 0 sur rxn rxn sur sys T H S S S S S sys S sur S univ Spontaneous? + + (exo) + yes - - (endo) - no + - (endo) ? yes if | S sys |>| S sur | (high T) - + (exo) ? yes if | S sys |<| S sur | (low T) Spontaneity and chemical rxns (T=298 o C, P=1atm)
Example: Phase transitions at T=const Calculate S sys for 1 mole of ice melting at room temperature T H T Q S ft r 1 1 1 0 . 22 273 012 , 6 K mol J K mol J T H S ft m 2. Short answer (8 points). Determine the sign of S sys , surr , and univ for an ice cube melting in water at T=0 O C and T=10 o C: H 2 O (ice) H 2 O (ice) H 2 O (liquid) T surr univ 0 o C + - 0 10 o C + - +

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4. Multiple choice (10 points). Consider the dissociation of hydrogen: H 2 (g) <=> 2H(g) A. For this reaction, the following is true (circle the correct answer): a) H >0, S>0 b) H>0, S<0 c) H<0, S>0 d) H<0, S<0 B. One would expect that this reaction (circle the correct answer) : a) will be spontaneous at any temperature. b) will be spontaneous at high temperatures. c) will be spontaneous at low temperatures. d) will not be spontaneous at any temperature. e) will never happen. G = H - T S Why S>0? More independent particles, more gases. Why exothermic? Need to break a chemical bond.

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monoclinic crystal form at temperatures above 95 C S rhombic S monoclinic A. Predict the signs of H and S for the process Explain your answer. B.
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ForExam4 - Exam#4 will cover Spontaneity and entropy...

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