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Thermodynamics

# Thermodynamics - Thermodynamics 1 For a process at 451 K...

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Thermodynamics 1. For a process at 451 K and constant pressure, S surr is -326 J K -1 . Calculate the quantity of heat (in kJ) absorbed by the system. 2. Which of the following produces an INCREASE in entropy of the system? a. H 2 O(l) --> H 2 O(s) b. 2O 2 (g) + 2SO(g) --> 2SO 3 (g) c. 2CH 3 OH(g) + 3O 2 (g) --> 2CO 2 (g) + 4H 2 O(l) d. I 2 (s) --> I 2 (l) e. None of the above. 3. The gas-phase reaction between H 2 and Cl 2 can be initiated by ultraviolet light at 25 o C, H 2 (g) + Cl 2 (g) --> 2HCl(g) Using the thermodynamic data provided below, calculate the standard free energy change (in kJ) at 25 o C for this reaction. compound H f o , kJ mol -1 S o , J mol -1 K -1 H 2 0 130.57 Cl 2 0 222.96 HCl -92.307 186.80 4. In lecture, you observed the following reaction, 2H 2 (g) + O 2 (g) --> 2H 2 O(g) For this reaction, H o = -241.8 kJ and S o = -88.8 J K -1 . Assuming that H o = H and S o = S at all temperatures, calculate the temperature (in K) at which this reaction would become non-spontaneous. 5. For a particular chemical reaction at 400 o C, G = -67 kJ. Calculate the time (in seconds) it will take for the reaction to reach completion. 6. For a particular chemical reaction, H o is positive and S o is negative. Which of the following statements about the spontaneity of the reaction under standard conditions is TRUE ? a. The reaction will be spontaneous only if the magnitude of H o is large enough to overcome the unfavorable entropy change. b. The reaction will be spontaneous only if the magnitude of S o is large enough to overcome the unfavorable enthalpy change. c. The reaction will be spontaneous regardless of the magnitudes of H o and S o . d. The reaction cannot be spontaneous. e. The reaction will be spontaneous only of G o is positive. 7. Which of the following is TRUE for an operating voltaic cell? a. G > 0 ; E = 0 b. G < 0 ; E < 0 c. G = 0 ; E > 0 d. G = 0 ; E = 0 e. G < 0 ; E > 0 8. Which of the following produces a DECREASE in entropy of the system? Hint: the system is shown in bold.

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9. Consider the following reaction and thermodynamic data, 2H 2 O 2 (aq) <==> 2H 2 O(l) + O 2 (g) substance H f o , kJ mol -1 S o , J mol -1 K -1 H 2 O 2 (aq) -191.17 143.9 H 2 O(l) -285.83 69.91 O 2 (g) 0 205.14 Calculate the value (in kJ) of G o at 25 o C.
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