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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 108

At 500 °C, F2 gas is stable and does not dissociate, but at 840 °C, some dissociation occurs: F2(g) ⇌ 2 F(g). A flask filled with 0.600 atm of F2 at 500 °C was heated to 840 °C, and the pressure at equilibrium was measured to be 0.984 atm. What is the equilibrium constant Kp for the dissociation of F2 gas at 840 °C?

Verified step by step guidance
1
Step 1: Write the balanced chemical equation for the dissociation of F2: F2(g) ⇌ 2 F(g).
Step 2: Define the initial pressure of F2 and the change in pressure due to dissociation. Initially, the pressure of F2 is 0.600 atm.
Step 3: Let x be the change in pressure of F2 that dissociates. At equilibrium, the pressure of F2 will be (0.600 - x) atm, and the pressure of F will be 2x atm.
Step 4: Use the total pressure at equilibrium (0.984 atm) to set up the equation: (0.600 - x) + 2x = 0.984.
Step 5: Solve for x to find the equilibrium pressures of F2 and F, then use these pressures to calculate the equilibrium constant Kp using the expression Kp = (P_F)^2 / (P_F2).

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 numerical value that expresses the ratio of the partial pressures of the products to the reactants at equilibrium for a given reaction at a specific temperature. For the reaction F2(g) ⇌ 2 F(g), Kp is calculated using the formula Kp = (P_F)^2 / (P_F2), where P_F and P_F2 are the equilibrium partial pressures of the products and reactants, respectively.
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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. In this case, increasing the temperature shifts the equilibrium position of the dissociation of F2 gas to favor the formation of F atoms, thus affecting the equilibrium constant.
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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, the total pressure of a gas mixture is the sum of the partial pressures of each individual gas. In this problem, understanding the initial and equilibrium partial pressures of F2 and F is crucial for calculating Kp and analyzing the dissociation reaction.
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