solution5_pdf - ig996 Homework 5 Lyon (53565) This...

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ig996 – Homework 5 – Lyon – (53565) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. This homework assignment is due Wednes- day, ±ebruary 20 at 4pm. 001 10.0 points ±or the reaction POCl 3 (g) POCl(g) + Cl 2 (g) K c = 0 . 30. An initial 0 . 33 moles oF POCl 3 are placed in a 2 . 1 L container with initial concentrations oF POCl and Cl 2 equal to zero. What is the fnal concentration oF POCl 3 ? ( Note: You must solve a quadratic equation.) 1. fnal concentration = 0 . 356143 M 2. fnal concentration = 0 . 0432435 M cor- rect 3. fnal concentration = 0 . 114 M 4. fnal concentration = 0 . 0864871 M 5. fnal concentration = 0 . 199 M Explanation: K c = 0.30 V container = 2 . 1 L [POCl 3 ] initial = 0 . 33 mol 2 . 1 L = 0 . 157143 M POCl 3 (g) POCl(g) + Cl 2 (g) ini, M 0 . 157143 - - Δ, M - x x x eq, M 0 . 157143 - x x x K c = [Cl 2 ][POCl] [POCl 3 ] = x 2 0 . 157143 - x = 0 . 3 x 2 = 0 . 0471429 - 0 . 3 x x 2 + 0 . 3 x - 0 . 0471429 = 0 x = - 0 . 3 ± r (0 . 3) 2 - 4 (1) ( - 0 . 0471429) 2 (1) = 0 . 113899 or - 0 . 413899 Reject - 0 . 413899 as x because it leads to negative concentrations For POCl and Cl 2 and a concentration larger that the orig- inal concentration For POCl 3 . ThereFore x = 0 . 113899 M and [POCl 3 ] = 0 . 157143 M - 0 . 113899 M = 0 . 0432435 M 002 10.0 points What happens to the concentration oF SO 2 (g) when the total pressure on the equi- librium reaction 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) is increased (by compression)? 1. decreases correct 2. remains the same 3. Unable to determine 4. increases 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 SO 2 will decrease. 003 10.0 points The reaction For the synthesis oF ammonia N 2(g) + 3 H 2(g) 2 NH 3(g) is exothermic. Increasing the temperature applied to the system I) increases the amount oF NH 3 . II) decreases the amount oF NH 3 . III) changes the value oF K eq . IV) does not change the value oF K eq .
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ig996 – Homework 5 – Lyon – (53565) 2 1. II and IV only 2. I and IV only 3. II and III only correct 4. I and III only Explanation: N 2(g) + 3 H 2(g) 2 NH 3(g) + Heat Heat or energy is a product of this reaction. If temperature of the system is increased then the reaction will proceed in the reverse di- rection until equilibrium is re-established (de- creasing NH 3 ). K eq is temperature dependent so changing the temperature will change K eq . 004
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