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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 81

Consider the reaction: H2(g) + I2(g) ⇌ 2 HI(g) A reaction mixture at equilibrium at 175 K contains PH2 = 0.958 atm, PI2 = 0.877 atm, and PHI = 0.020 atm. A second reaction mixture, also at 175 K, contains PH2 = PI2 = 0.621 atm and PHI = 0.101 atm. Is the second reaction at equilibrium? If not, what will be the partial pressure of HI when the reaction reaches equilibrium at 175 K?

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Key Concepts

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

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this state, the system appears static, but molecular activity continues. The equilibrium constant (K) quantifies the ratio of product concentrations to reactant concentrations at equilibrium, providing insight into the position of equilibrium.
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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 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 a chemical reaction.
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Partial Pressure and the Ideal Gas Law

Partial pressure refers to the pressure exerted by an individual gas in a mixture, which can be calculated using Dalton's Law of Partial Pressures. The Ideal Gas Law (PV=nRT) relates the pressure, volume, and temperature of a gas, allowing for the determination of the behavior of gases under various conditions. Understanding these concepts is crucial for calculating equilibrium concentrations in gas-phase reactions.
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