Reaction Quotient and Le Châtelier’s Principle
Caleb Thomas
6 min read
Study Guide Overview
This study guide explains Le Châtelier's Principle using the reaction quotient (Q). It reviews how Q relates to the equilibrium constant (K) and how to use it to predict equilibrium shifts due to changes in concentration and pressure. It also covers how temperature affects equilibrium by changing K, and emphasizes the importance of stoichiometry when dealing with pressure changes. The guide includes practice questions and exam tips.
#Le Châtelier's Principle: Why It Works (Using Q)
Hey there, future AP Chem master! 👋 Ready to dive deeper into Le Châtelier's Principle? Last time, we used logic to predict shifts in equilibrium. Now, let's see how the reaction quotient, Q, justifies these shifts. This is your go-to guide for understanding the why behind the what.
#Review of the Reaction Quotient, Q
Remember Q, the reaction quotient? It's like a snapshot of your reaction at any given moment, not just at equilibrium.
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Q tells us which way a reaction will shift to reach equilibrium.
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If Q < K, the reaction shifts towards products.
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If Q > K, the reaction shifts towards reactants.
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If Q = K, the system is at equilibrium.
Key Point: The formulas for Q and K are the same, but Q can be calculated at any concentration, while K is only at equilibrium. Reactions will always proceed in the direction that makes Q = K.
#Applying Q to Le Châtelier's Principle
#Concentration
Changing concentrations messes with the balance, and Q helps us see how the system responds.
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Adding products increases the numerator of Q, making Q > K. The system shifts to the reactants.
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Adding reactants increases the denominator of Q, making Q < K. The system shifts to the products.
Image: Reaction quotient (Q) vs. equilibrium constant (K). Notice how the system shifts to make Q = K.
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