chem_126_2010_Common_3_ANSWERSw332q1zzz0nw

chem_126_2010_Common_3_ANSWERSw332q1zzz0nw - Chem 126...

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Chem 126 Common 3 Part I April, 23, 2010 ANSWERS 1. What is the oxidation state of phosphorus in 2 4 HPO - ? (a) 1 (b) 2 (c) 3 (d) 5 (e) 7 2. Which of the following statements about entropy is false? (a) The standard entropy of formation of N 2 is zero. (b) Entropy and heat capacity have the same units. (c) The entropy decreases for the reaction 2H 2 (g) + O 2 (g) 2H 2 O(l). (d) The entropy of a sugar cube and water is smaller than the entropy of the sugar cube dissolved in the water. (e) The entropy of C 2 F 4 is smaller than the entropy of C 2 F 4 H 2 . 3. Which of the following processes is NOT ALWAYS spontaneous? (a) The voltage of the reaction is positive. (b) The change in free energy of a reaction is negative. (c) The reaction is exothermic. (d) Q for a reaction is less than the equilibrium constant. (e) At constant pressure, H rxn > 0 (endothermic), S rxn > 0 and T is very large. 4. What is w when E = -1,500 J and 2,000 J of heat are added? (a) 3,500 J (b) -3,500 J (c) 500 J (d) -500 J (e) none of the above ( 29 ( 29 ( 29 2 4 2 136 ; 235 / o rxn C s Cl g CCl g H kJ S J K + = - ∆ = - 5. Calculate o rxn G for the above reaction at 200 o C. (a) 1.11x10 5 kJ (b) -25 kJ (c) 99 kJ (d) -99 kJ (e) -371 kJ 6. Above about what temperature is the above reaction no longer spontaneous? (Pick closest.) (a) 400 K (b) 500 K (c) 600 K (d) 700 K (e) 800 K 1,500 2,000 3,500 E q w w E q J = + = ∆ - = - - = - The entropy is only zero for a perfect crystal at absolute zero. ( 29 1, 2, : 1 4 2 2; 5 H O P x x x = + = - = + + - = - = 0 for large T and 0 rxn rxn rxn rxn G H T S S = ∆ - ∆ < ( 29 3 235 1 136 200 273 25 10 o o o J kJ G H T S kJ K kJ K kJ - = ∆ - ∆ = - - + = - 136,000 0 ; 579 235 / o o o o o H J G H T S T K S J K - = = ∆ - ∆ = = = -
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7. Calculate the free energy of formation for ethane, C 2 H 6 . 1,467 o rxn G kJ = - for the following reaction: C 2 H 6 (g) + 3.5O 2 (g) 2CO 2 (g) + 3H 2 O (l ) (a) None of the below (b) 836 kJmol -1 (c) -836 kJmol -1 (d) 32 kJmol -1 (e) -32 kJmol -1 8. 50. g of iron at 90ºC is placed in 40. g of water at 20ºC. What is the equilibrium temperature? The specific heat of iron is about 0.45 J/g/ºC and water's is about 4.18 J/g/ºC. (a) 22 o C (b) 24 o C (c) 26 o C (d) 28 o C (e) >30 o C 9. What is the voltage of the following reaction for standard conditions: (a) 0.67 V (b) 1.73 V (c) 0.93 V (d) -1.73 V (e) -0.93 V 10. For the Zn-H 2 Galvanic cell, ( 29 ( 29 ( 29 2 2 ( ) 2 0.76 Zn s H aq Zn aq H g E V ο + + + → + + = , which statement is
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This note was uploaded on 11/09/2010 for the course CHEM Chem taught by Professor Petrova during the Spring '09 term at NJIT.

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chem_126_2010_Common_3_ANSWERSw332q1zzz0nw - Chem 126...

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