17 Equilibrium Applications

17 Equilibrium Applications - A sample of PCl5 gas is...

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1 1 A sample of PCl 5 gas is introduced into a flask at 250 o C at a pressure of exactly 1 atm, but some of this gas decompose to PCl 3 and Cl 2 to produce an equilibrium total pressure of 1.98 atm. What is the value of the equilibrium constant, K p , for this reaction? PCl 5 (g) PCl 3 (g) + Cl 2 (g) A) 50 atm B) 1.98 atm C) 48 atm D) 2.0 atm Partial pressure is proportional to moles and concentration, so you can work with partial pressures just like using moles or concentration. Construct the RICE table. Let x = partial pressure of PCl 5 that decomposes. Solve for x using the equilibrium total pressure. Substitute into the K p expression to find K p . 2 PCl 5 (g) PCl 3 (g) + Cl 2 (g) 1 atm 0 0 -x +x +x 1 atm – x x x 2 2 1 1 2 1.98 1.98 1 0.98 (.98) 48 .02 p p x K x xx x K atm     One equation in two unknowns (K p & x ), need another equation. The total final pressure was 1.98 atm.

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2 3 QRT 14.42: Butane (B) and 2-methypropane (MP) can convert from one isomer to the other. At 25 o C, K C = 2.5 for this reaction. If 0.50 mole of each isomer were put in a 10.0 L container at 25 o C, what would the ratio of the concentrations be at equilibrium? Report equilibrium [MP]/[B] = A) 1.0 B) 2.0 C) 2.5 D) 5.0 K C = [MP] / [B] = 2.5 BM P Note: This problem will reward those who understand. 4 MSJ p. 693, PSE 14.7 Use of the Quadratic Formula An equilibrium problem often will produce a quadratic equation. The solution is given by the quadratic formula. See MSJ p. 693, PSE 14.7. Do MSJ p. 694, PSP 14.7. 2a 4ac - b b - x 0 c bx ax x) - x)(n - (m x K 2 2 When x is not negligible, compared to m and n. How to tell? At the beginning: K > 10 –3 Check at the end: x > m or n /20
3 5 Today’s To Do Use Le Chatelier’s Principle to predict shifts in equilibria. Calculate values for equilibrium constants at different temperatures using thermodynamic data. Explain why high temperatures and pressures are necessary for the industrial production of ammonia.

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This note was uploaded on 03/29/2010 for the course CHE 132 taught by Professor Hanson during the Spring '08 term at SUNY Stony Brook.

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17 Equilibrium Applications - A sample of PCl5 gas is...

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