CHEM31PracticeProblemsCh10

CHEM31PracticeProblemsCh10 - a values. (b) From the...

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CHEM 31 Additional Practice Problems Free Energy, Equilibrium, and Spontaneity I. (Combining free energy, equilibrium, and kinetics) Consider the reaction: 2NO (g) + O 2 (g) 2NO 2 (g) Thermochemical Information (at 298K): G o f (kJ/mol) H o f (kJ/mol) S o (J/K mol) NO 86.7 90.4 210.6 O 2 0 0 205.0 NO 2 51.8 33.85 240.46 a. The forward rate constant for the above reaction is 7.1x10 9 M -2 s -1 at 25 o C. Assuming a simple one-step mechanism, what is the rate constant for the reverse reaction? (Hint: first find K eq at 25 o C and then find k -1 .) b. What is K for the above reaction at 500K assuming H o f and S o are temperature independent?
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II. (Combining Free Energy, equilibrium, and acid-base chemistry.) Consider two carboxylic acids (acids that contain the –COOH group): CH 3 COOH (acetic acid, K a = 1.8 x 10 -5 ) and CH 2 ClCOOH (chloroacetic acid, K a = 1.4 x 10 -3 ). (a) Calculate Δ Gº for the ionization of these acids at 25ºC using the K
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Unformatted text preview: a values. (b) From the equation Δ Gº = Δ Hº – T Δ Sº, we see that the contributions to the Δ Gº term are an enthalpy term ( Δ Hº) and a temperature times entropy term (T Δ Sº). These contributions are listed below for the two acids: Which is the dominant term in determining the value of Δ Gº (and hence K a of the acid)? (c) What processes contribute to Δ Hº? (Consider the ionization of the acids as a Bronsted acid-base reaction and think about bonds that are broken and formed.) (d) Propose a reason why T Δ Sº is more negative for CH 3 COOH. (Hint: ions in aqueous solutions have a tendency to order the dipolar water molecules surrounding them, with the extent of the ordering being greater for smaller ions.) Δ Hº (kJ) T Δ Sº (kJ) CH 3 COOH -0.57 -27.6 CH 2 ClOOH -4.7 -21.1...
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This note was uploaded on 12/05/2011 for the course CHEMISTRY 31 taught by Professor Roy during the Fall '09 term at Duke.

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CHEM31PracticeProblemsCh10 - a values. (b) From the...

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