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17 Equilibrium Applications

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

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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 x x x K atm One equation in two unknowns, need another equation. The total final pressure was 1.98 atm.

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