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Solving Equilibrium problems using the RICE method

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General Method 1.Write the balanced equation for the reaction. 2.Write the equilibrium expression using the law of mass action. 3.List the initial concentrations. 4.Calculate Q to determine the shift to equilibrium. 5.Define the change needed to reach equilibrium. 6.Substitute equilibrium concentrations and solve for the unknown.

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Solving for Equilibrium Concentration Consider this reaction at some temperature: H 2 O(g) + CO(g) H 2 (g) + CO 2 (g) K = 2.0 Assume you start with 8 molecules of H 2 O and 6 molecules of CO. How many molecules of H 2 O, CO, H 2, and CO 2 are present at equilibrium? “ICE” Here, we learn about “ICE” – the most important problem solving technique in the second semester. You will use it for the next 4 chapters!

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Solving for Equilibrium Concentration H 2 O(g) + CO(g) H 2 (g) + CO 2 (g) K = 2.0 Step #1: We write the law of mass action for the reaction:

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Solving for Equilibrium Concentration H 2 O(g) + CO(g) H 2 (g) + CO 2 (g) Initial: Change: Equilibri um: Step #2: We “ICE” the problem, beginning with the Initial concentrations 8600 -x +x 8-x6-x x x

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Solving for Equilibrium Concentration Equilibri um: 8-x6-xxx Step #3: We plug equilibrium concentrations into our equilibrium expression, and solve for x H 2 O(g) + CO(g) H 2 (g) + CO 2 (g)

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Solving for Equilibrium Concentration Step #4: Substitute x into our equilibrium concentrations to find the actual concentrations H 2 O(g) + CO(g) H 2 (g) + CO 2 (g) Equilibri um: 8-x6-xxx Equilibri um: 8-4=46-4=244

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At a particular temperature, K p = 0.25 for the reaction N 2 O 4 2NO 2 A flask containing only N 2 O 4 at an initial pressure of 4.5 atm is allowed to reach equilibrium. Calculate the equilibrium partial pressures of the gases.

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At a particular temperature, K p = 0.25 for the reaction N 2 O 4 2NO 2 A flask containing only NO 2 at an initial pressure of 9.0 atm is allowed to reach equilibrium. Calculate the equilibrium partial pressures of the gases.

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Carbon monoxide reacts with steam to produce carbon dioxide and hydrogen. At 700 K, the equilibrium constant is 5.10. Calculate the equilibrium concentrations of all species if 3.00 mol of each component is mixed in 2.000 L flask. CO (g) + H2O (g) CO2 (g) + H2 (g)

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