mccord exam 2 solutions

mccord exam 2 solutions - Version 142 – Exam 2 – McCord...

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Unformatted text preview: Version 142 – Exam 2 – McCord – (52405) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Make sure you are taking the right exam. This is Dr. McCord’s 10AM CH302 course with unique 52405. McCord 10am 001 10.0 points What happens to the concentration of NO(g) when the total pressure on the equilib- rium reaction 3 NO 2 (g) + H 2 O( ℓ ) ⇀ ↽ 2 HNO 3 (aq) + NO(g) is increased (by compression)? 1. Unable to determine 2. decreases 3. increases correct 4. remains the same Explanation: Increasing the total pressure on the sys- tem by decreasing its volume will shift the equilibrium toward the side of the reaction with fewer numbers of moles of gaseous com- ponents. If the total number of moles of gas is the same on the product and reactant sides of the balanced chemical equation, then changing the pressure will have little or no ef- fect on the equilibrium distribution of species present. The amount and concentration of NO will increase. 002 10.0 points If Δ G ◦ rxn is positive, then the forward reaction is (spontaneous / nonspontaneous) and K is (less / greater) than one. 1. nonspontaneous; greater 2. spontaneous, less 3. spontaneous, greater 4. None of these; Δ G is not directly related to K . 5. nonspontaneous; less correct Explanation: A positive Δ G ◦ rxn (standard reaction free energy) denotes an endothermic reation, which is nonspontaneous. Also, Δ G ◦ rxn =- RT ln K , so a positive Δ G ◦ rxn would result in a K that is between the values of zero and one. 003 10.0 points A weak acid (HA) is found to ionize 17% when mixed at a concentration of 0 . 38 mol/L. What is the value of K a for this acid? 1. 0.00952941 2. 0.00994147 3. 0.0170042 4. 0.00967314 5. 0.0266667 6. 0.00935926 7. 0.00483024 8. 0.0132313 9. 0.00678571 10. 0.00555464 Correct answer: 0 . 0132313. Explanation: . 17(0 . 38) = 0 . 0646 . You must also subtract that amount from the original concentration, too: . 38- . 0646 = 0 . 3154 K a = (0 . 0646) 2 . 3154 = 0 . 0132313 . 004 10.0 points 100 mL of 0.50 M BaCl 2 is added to 100 mL of 0.50 M HCl. Which of the following equations is the correct charge balance for this system? 1. 2[Ba 2+ ] = [Cl − ] 2. 2[Ba 2+ ] + [H + ] = 2[OH − ] + 2[Cl − ] Version 142 – Exam 2 – McCord – (52405) 2 3. 2[Ba 2+ ] + [H + ] = 2[OH − ] + [Cl − ] 4. [Ba 2+ ] + [H + ] = 3[Cl − ] 5. 2[Ba 2+ ] + [H + ] = [OH − ] + [Cl − ] correct 6. [Ba 2+ ] = 2[OH − ] 7. [Ba 2+ ] + [H + ] = [OH − ] + [Cl − ] Explanation: 005 10.0 points Consider the statements Z1) A 0.05 M HCl solution has the same pH as 0.05 M HCN. Z2) A 0.10 M solution of a weak acid has the same pH as a 0.10 M solution of a weak base that has the same ionization constant....
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This note was uploaded on 09/28/2009 for the course GE 206E taught by Professor staff during the Spring '09 term at University of Texas.

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mccord exam 2 solutions - Version 142 – Exam 2 – McCord...

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