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Chem2 hw3s - Yoon Seong Meen – Homework 3 – Due 11:00...

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Yoon, Seong Meen – Homework 3 – Due: Sep 26 2007, 11:00 pm – Inst: James Holcombe 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points The reaction A + B * ) C + 2 D has an equilibrium constant of 3 . 7 × 10 - 3 . Consider a reaction mixture with [A] = 2 . 0 × 10 - 2 M [B] = 1 . 7 × 10 - 4 M [C] = 2 . 4 × 10 - 6 M [D] = 3 . 5 × 10 - 3 M Which of the following statements is defi- nitely true? 1. The reverse reaction can occur to a greater extent than the forward reaction until equilibrium is established. 2. Heat will be evolved. 3. The forward reaction can occur to a greater extent than the reverse reaction until equilibrium is established. correct 4. No conclusions about the system can be made without additional information. 5. The system is at equilibrium. Explanation: Q = [C] [D] 2 [A] [B] = (2 . 4 × 10 - 6 M) (0 . 0035 M) 2 (0 . 02 M) (0 . 00017 M) = 8 . 64706 × 10 - 6 Since Q < K the foward reaction is favored. 002 (part 1 of 1) 10 points Write the equilibrium constant for 2 NaBr(aq) + Pb(ClO 4 ) 2 (aq) PbBr 2 (s) + 2 NaClO 4 (aq) . 1. K = 1 [Pb(ClO 4 ) 2 ][NaBr] 2 2. K = [Pb 2+ ][Br - ] 2 3. K = [PbBr 2 ] [Pb 2+ ][Br - ] 2 4. K = 1 [Pb 2+ ][Br - ] 2 correct 5. K = [NaClO 4 ] 2 [NaBr] 2 [Pb(ClO 4 ) 2 ] Explanation: 003 (part 1 of 1) 10 points An equilibrium in which processes occur con- tinuously, with NO NET change, is called 1. hetergeneous equilibrium. 2. dynamic equilibrium. correct 3. homogeneous equilibrium. 4. static equilibrium. Explanation: In dynamic equilibrium the forward and re- verse processes of the system continue but be- cause their rates are equal there is no change in the composition of the system. 004 (part 1 of 1) 10 points The expression for K c for the reaction at equi- librium is 4 NH 3 (g) + 5 O 2 (g) * ) 4 NO(g) + 6 H 2 O(g) 1. [NO] 4 [H 2 O ] 6 2. [NH 3 ] 4 [O 2 ] 5 [NO] 4 [H 2 O] 6 3. [NH 3 ] 4 [O 2 ] 5 4. [NO] 4 [H 2 O] 6 [NH 3 ] 4 [O 2 ] 5 correct Explanation: The equation must be written with the ap- propriate formula and correctly balanced. K c is the equilibrium constant for species in so- lution and equals the mathematical product
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Yoon, Seong Meen – Homework 3 – Due: Sep 26 2007, 11:00 pm – Inst: James Holcombe 2 of the concentrations of the chemical prod- ucts, divided by the mathematical product of the concentrations of the chemical reactants. In this mathematical expression, each concen- tration is raised to the power of its coefficient in the balanced equation. For K c the molar concentrations are used for the activities of the components. 005 (part 1 of 1) 10 points The equilibrium constant for the reaction 2 SO 2 (g) + O 2 (g) * ) 2 SO 3 (g) has the value K = 2 . 5 × 10 10 at 500 K. Find the value of K for the reaction SO 2 (g) + 1 2 O 2 (g) * ) SO 3 (g) at the same temperature.
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