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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 46

At 900 K, the following reaction has 𝐾𝑝 = 0.345: 2 SO2(𝑔) + O2(𝑔) β‡Œ 2 SO3(𝑔) In an equilibrium mixture the partial pressures of SO2 and O2 are 0.135 atm and 0.455 atm, respectively. What is the equilibrium partial pressure of SO3 in the mixture?

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1
Write the expression for the equilibrium constant, Kp, for the reaction. For the reaction 2 SO2(g) + O2(g) β‡Œ 2 SO3(g), the expression is Kp = (P_SO3)^2 / ((P_SO2)^2 * P_O2).
Substitute the given values of the partial pressures of SO2 and O2 into the Kp expression. Here, P_SO2 = 0.135 atm and P_O2 = 0.455 atm.
Rearrange the Kp expression to solve for P_SO3. This involves isolating P_SO3 on one side of the equation.
Take the square root of both sides of the equation to solve for P_SO3, since P_SO3 is squared in the Kp expression.
Ensure that the units are consistent and that the calculation is dimensionally correct to find the equilibrium partial pressure of SO3.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Equilibrium Constant (Kp)

The equilibrium constant, Kp, is a dimensionless number that expresses the ratio of the partial pressures of products to reactants at equilibrium for a given reaction at a specific temperature. For the reaction 2 SO2(g) + O2(g) β‡Œ 2 SO3(g), Kp is calculated using the formula Kp = (P_SO3^2) / (P_SO2^2 * P_O2), where P represents the partial pressures of the gases involved. A Kp value less than 1 indicates that at equilibrium, the reactants are favored over the products.
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Partial Pressure

Partial pressure is the pressure exerted by a single component of a gas mixture. According to Dalton's Law of Partial Pressures, the total pressure of a gas mixture is the sum of the partial pressures of each individual gas. In this context, knowing the partial pressures of SO2 and O2 allows us to calculate the partial pressure of SO3 at equilibrium using the equilibrium constant.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust itself to counteract the change and restore a new equilibrium. This principle helps predict how changes in concentration, pressure, or temperature will affect the position of equilibrium. In this case, understanding how the equilibrium shifts can provide insights into the relationship between the partial pressures of the reactants and products.
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