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University of Texas CH 302 McCord H05 - Equilibrium 2

# University of Texas CH 302 McCord H05 - Equilibrium 2 -...

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byrne (cmb3744) – H05: Equilibrium 2 – mccord – (51620) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A 2.000 liter vessel is filled with 4.000 moles of SO 3 and 6.000 moles of O 2 . When the reaction 2 SO 3 (gas) 2 SO 2 (gas) + O 2 (gas) comes to equilibrium a measurement shows that only 1.000 mole of SO 3 remains. How many moles of O 2 are in the vessel at equilib- rium? 1. 7.000 mol 2. 7.500 mol correct 3. None of these is correct. 4. 12.000 mol 5. 3.750 mol Explanation: Initially, [SO 3 ] = 4 mol 2 L = 2 M [O 2 ] = 6 mol 2 L = 3 M 2 SO 3 (g) 2 SO 2 (g) + O 2 (g) ini, M 2 0 3 Δ, M - 2 x 2 x x eq, M 2 - 2 x 2 x 3 + x At equilibrium, [SO 3 ] eq = 1 mol 2 L = 0 . 5 M, so 2 - 2 x = 0 . 5 - 2 x = - 1 . 5 x = 0 . 75 Thus [O 2 ] = 3 + x = 3 . 75 M mol O 2 = (3 . 75 mol / L) (2 L) = 7 . 5 mol . 002 10.0points Suppose the reaction A B has an equilibrium constant of 1.0 and the ini- tial concentrations of A and B are 0.5 M and 0.0 M, respectively. Which of the following is the correct value for the final concentration of A? 1. 0.250 M correct 2. None of these is correct. 3. 1.50 M 4. 1.00 M 5. 0.500 M Explanation: K = 1 . 0 [A] ini = 0 . 5 M [B] ini = 0 M A B ini, M 0.5 0.0 Δ, M - x x eq, M 0 . 5 - x x K = [B] [A] = 1 . 0 x 0 . 5 - x = 1 . 0 x = 0 . 25 M [A] = 0 . 5 - x = 0 . 25 M 003 10.0points Suppose the reaction H 2 (g) + I 2 (g) 2 HI(g) has an equilibrium constant K c = 49 and the initial concentration of H 2 and I 2 is 0.5 M and HI is 0.0 M. Which of the following is the correct value for the final concentration of HI(g)? 1. 0.599 M

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byrne (cmb3744) – H05: Equilibrium 2 – mccord – (51620) 2 2. 0.778 M correct 3. 0.250 M 4. 0.389 M 5. 0.219 M Explanation: K c = 49 [H 2 ] ini = 0 . 5 M [I 2 ] ini = 0 . 5 M [HI] ini = 0 M H 2 (g) + I 2 (g) 2 HI(g) Ini, M 0.5 0.5 0 Δ, M - x - x +2 x Equil, M 0 . 5 - x 0 . 5 - x 2 x K c = [HI] 2 [H 2 ] [I 2 ] 49 = (2 x ) 2 (0 . 5 - x ) 2 7 = 2 x 0 . 5 - x 7(0 . 5 - x ) = 2 x 3 . 5 - 7 x = 2 x 3 . 5 = 9 x x = 3 . 5 9 = 0 . 389 M Looking back at our equilibrium values, we see that the final concentration of HI is equal to 2 x , so 2(0.389) = 0.778 M. 004 10.0points At T = 600 C, K c = 1 for the gas-phase reaction A + B C + D Starting with 1 . 98 moles each of A and B in a 5.00 liter container, what will be the equilib- rium concentration of C at this temperature? Correct answer: 0 . 198 M. Explanation: [A] = 1 . 98 mol 5 L = 0 . 396 M T = 600 C [B] = 1 . 98 mol 5 L = 0 . 396 M K c = 1 A + B C + D ini, M 0 . 396 0 . 396 0 0 Δ, M - x - x x x eq, M 0 . 396 - x 0 . 396 - x x x [C][D] [A][B] = 1 x 2 (0 . 396 - x ) 2 = 1 x 0 . 396 - x = 1 x = 0 . 396 - 1 x x = [C] = 0 . 198 M 005 10.0points The system H 2 (g) + I 2 (g) 2 HI(g) is at equilibrium at a fixed temperature with a partial pressure of H 2 of 0.200 atm, a partial pressure of I 2 of 0.200 atm, and a partial pres- sure of HI of 0.100 atm. An additional 0 . 15 atm pressure of HI is admitted to the con- tainer, and it is allowed to come to equilib- rium again. What is the new partial pressure of HI?
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