Chemical equilibrium constants, reaction quotient, and Le Chatelier's principle for predicting shifts in equilibrium tested on the MCAT.
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- What does the equilibrium constant, Keq, describe about a reversible reaction?
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The ratio of product concentrations to reactant concentrations, each raised to their stoichiometric coefficients, at equilibrium
- What does a large Keq value (much greater than 1) indicate about a reaction at equilibrium?
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Products are favored at equilibrium
- What does a small Keq value (much less than 1) indicate about a reaction at equilibrium?
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Reactants are favored at equilibrium
- What is the reaction quotient, Q, used for?
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Determining the direction a reaction will shift to reach equilibrium by comparing it to Keq
- If Q is less than Keq, in which direction will the reaction proceed?
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Forward, toward products
- If Q is greater than Keq, in which direction will the reaction proceed?
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Reverse, toward reactants
- What does Le Chatelier's principle state about a system at equilibrium subjected to a stress?
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The system will shift in the direction that relieves the stress and restores equilibrium
- According to Le Chatelier's principle, how does adding more reactant to a system at equilibrium shift the reaction?
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It shifts the equilibrium toward the products
- According to Le Chatelier's principle, how does removing product from a system at equilibrium shift the reaction?
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It shifts the equilibrium toward the products to replace what was removed
- According to Le Chatelier's principle, how does increasing pressure by decreasing volume shift a gas-phase equilibrium?
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It shifts the equilibrium toward the side with fewer moles of gas
- According to Le Chatelier's principle, how does an increase in temperature shift an exothermic reaction at equilibrium?
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It shifts the equilibrium toward the reactants, since heat is treated as a product
- According to Le Chatelier's principle, how does an increase in temperature shift an endothermic reaction at equilibrium?
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It shifts the equilibrium toward the products, since heat is treated as a reactant
- Does adding a catalyst shift the position of equilibrium?
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No, a catalyst speeds up both forward and reverse reactions equally and does not shift equilibrium
- What effect does a catalyst have on the equilibrium constant, Keq?
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None; a catalyst does not change the value of Keq
- What is the solubility product constant, Ksp, used to describe?
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The equilibrium between a solid ionic compound and its dissolved ions in a saturated solution