AP Chemistry Flashcards: Reaction Quotient And Le Chateliers Principle

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This deck focuses on Reaction Quotient And Le Chateliers Principle, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What does $Q_c = K_c$ signify?

Answer: The system is at equilibrium. When $Q_c$ equals $K_c$, forward and reverse reaction rates are equal.

Flashcard 2: Define Le Chatelier's Principle.

Answer: A system at equilibrium will adjust to counteract imposed changes. The system responds to minimize the disturbance and restore balance.

Flashcard 3: What does $Q_c > K_c$ suggest about reaction direction?

Answer: The reaction will proceed in the reverse direction. When $Q_c > K_c$, excess products convert back to reactants.

Flashcard 4: What is the effect of removing a product from a reaction at equilibrium?

Answer: The equilibrium shifts to the right to form more products. System compensates by producing more of the removed product.

Flashcard 5: State what happens to equilibrium if a catalyst is added.

Answer: The rate increases, but equilibrium position is unchanged. Catalysts affect kinetics but not the equilibrium position.

Flashcard 6: How does adding an inert gas at constant volume affect equilibrium?

Answer: There is no effect on the position of equilibrium. Inert gas doesn't change partial pressures of reactants or products.

Flashcard 7: How does removing a reactant affect the position of equilibrium?

Answer: The equilibrium shifts to the left, forming more reactants. System produces more reactant to replace what was removed.

Flashcard 8: What is the effect of temperature decrease on the $K_c$ of an endothermic reaction?

Answer: $K_c$ decreases with a decrease in temperature. Lower temperature opposes endothermic reactions, decreasing $K_c$.

Flashcard 9: What defines the direction of shift when pressure is increased in a gaseous reaction?

Answer: Shifts to the side with fewer moles of gas. Higher pressure favors the side with fewer gas molecules.

Flashcard 10: What effect does increasing pressure have on a gaseous equilibrium?

Answer: The equilibrium shifts towards the side with fewer moles of gas. Higher pressure favors the side with fewer gas molecules.

Flashcard 11: Calculate $Q_c$ for $2A \rightleftharpoons B$ if $[A] = 0.3$, $[B] = 0.2$.

Answer: $Q_c = \frac{[B]}{[A]^2} = \frac{0.2}{0.3^2} = 2.22$. Substitute the given concentrations into the $Q_c$ expression.

Flashcard 12: How does increasing reactant concentration affect equilibrium position?

Answer: Shifts right, forming more products. More reactant drives the equilibrium forward to consume it.

Flashcard 13: What happens to equilibrium when a product concentration is decreased?

Answer: The equilibrium shifts to the right to produce more product. System compensates by producing more of the removed product.

Flashcard 14: What is the effect of adding a strong acid to a weak acid equilibrium?

Answer: The equilibrium shifts to the left, decreasing dissociation. Added acid increases $H^+$ concentration, suppressing weak acid dissociation.

Flashcard 15: What is the effect of temperature increase on the equilibrium constant for exothermic reactions?

Answer: The equilibrium constant, $K_c$, decreases. Higher temperature opposes exothermic reactions, reducing $K_c$.

Flashcard 16: What is the value of $Q_c$ if $[A] = 2$, $[B] = 3$, $[C] = 1$, $[D] = 4$ for $A + 2B \rightleftharpoons C + D$?

Answer: $Q_c = \frac{[C][D]}{[A][B]^2} = \frac{1 \times 4}{2 \times 3^2} = \frac{2}{9}$. Substitute concentrations into $Q_c$ expression and calculate.

Flashcard 17: Calculate $Q_c$ for a reaction if $[A] = 1.0$, $[B] = 2.0$, $[C] = 1.5$ for $A + B \rightleftharpoons C$.

Answer: $Q_c = \frac{[C]}{[A][B]} = \frac{1.5}{1.0 \times 2.0} = 0.75$. Apply the $Q_c$ formula using the given concentration values.

Flashcard 18: What is the effect of increasing volume on a gaseous equilibrium?

Answer: The equilibrium shifts to the side with more moles of gas. Increased volume decreases pressure, favoring more gas molecules.

Flashcard 19: Identify the effect of adding more product to an equilibrium system.

Answer: The equilibrium shifts to the left, producing more reactants. Excess product drives the equilibrium backward to consume it.

Flashcard 20: State the expression for $Q_c$ for $3A \rightleftharpoons 2B + C$.

Answer: $Q_c = \frac{[B]^2[C]}{[A]^3}$. Products in numerator, reactants in denominator with stoichiometric coefficients.

Flashcard 21: Which direction does equilibrium shift when a reactant concentration decreases?

Answer: The equilibrium shifts to the left, forming more reactants. System compensates by producing more of the depleted reactant.

Flashcard 22: How does temperature decrease affect $K_c$ in endothermic reactions?

Answer: $K_c$ decreases with a decrease in temperature. Lower temperature opposes endothermic reactions, decreasing $K_c$.

Flashcard 23: What happens to equilibrium when an aqueous solution is diluted?

Answer: The equilibrium shifts to the side with more solute particles. Dilution favors the side that produces more dissolved particles.

Flashcard 24: How does increasing the concentration of a reactant affect equilibrium?

Answer: The equilibrium shifts to the right, forming more products. System responds by consuming the excess reactant to form products.

Flashcard 25: Calculate $Q_c$ for $A + B \rightleftharpoons 2C$ if $[A] = 0.5$, $[B] = 0.5$, $[C] = 0.1$.

Answer: $Q_c = \frac{[C]^2}{[A][B]} = \frac{0.1^2}{0.5 \times 0.5} = 0.04$. Substitute given concentrations into the $Q_c$ formula.

Flashcard 26: How does the presence of a catalyst alter the rate of reaction?

Answer: A catalyst increases the rate of reaction without shifting equilibrium. Catalysts only affect reaction kinetics, not thermodynamic equilibrium.

Flashcard 27: What happens when $Q_c$ is less than $K_c$?

Answer: The reaction proceeds forward to reach equilibrium. When $Q_c < K_c$, forward reaction proceeds to reach equilibrium.

Flashcard 28: What happens to $K_c$ in an exothermic reaction if temperature decreases?

Answer: $K_c$ increases with a decrease in temperature. Lower temperature favors exothermic reactions, increasing $K_c$.

Flashcard 29: What is the effect of a catalyst on the position of equilibrium?

Answer: A catalyst does not affect the position of equilibrium. Catalysts speed up both forward and reverse reactions equally.

Flashcard 30: How does the addition of an inert gas at constant pressure affect equilibrium?

Answer: It changes the equilibrium position depending on moles of gas. At constant pressure, inert gas causes volume expansion affecting equilibrium.

Flashcard 31: How does decreasing temperature affect an exothermic reaction at equilibrium?

Answer: The equilibrium shifts to the right, favoring product formation. Lower temperature favors the exothermic direction (forward).

Flashcard 32: What does $Q_c < K_c$ indicate about reaction direction?

Answer: The reaction will proceed forward to reach equilibrium. When $Q_c < K_c$, more products must form to reach equilibrium.

Flashcard 33: What does $Q_c > K_c$ suggest about reaction direction?

Answer: The reaction will proceed in the reverse direction. When $Q_c > K_c$, excess products convert back to reactants.

Flashcard 34: What happens when $Q_c$ is less than $K_c$?

Answer: The reaction proceeds forward to reach equilibrium. When $Q_c < K_c$, forward reaction proceeds to reach equilibrium.

Flashcard 35: How does decreasing pressure affect a reaction with equal moles of gas on both sides?

Answer: There is no effect on the position of equilibrium. Pressure changes don't affect equilibrium when gas moles are equal.

Flashcard 36: Identify the change in equilibrium with an increase in product pressure.

Answer: The equilibrium shifts to the left, forming more reactants. Increased product concentration drives the reaction backward.

Flashcard 37: Define the reaction quotient, $Q_c$.

Answer: The ratio of product concentrations to reactant concentrations at any point. Measures current concentration ratio, not necessarily at equilibrium.

Flashcard 38: What is the effect of temperature increase on an endothermic reaction at equilibrium?

Answer: The equilibrium shifts to the right, favoring product formation. Higher temperature favors the endothermic direction (forward).

Flashcard 39: State the reaction quotient expression for $2A + B \rightleftharpoons 3C + D$.

Answer: $Q_c = \frac{[C]^3[D]}{[A]^2[B]}$. Products in numerator with coefficients as exponents, reactants in denominator.

Flashcard 40: What happens to $K_c$ with temperature change in an exothermic reaction?

Answer: $K_c$ decreases with an increase in temperature. Higher temperature opposes exothermic reactions, decreasing $K_c$.

Flashcard 41: What effect does temperature have on $K_c$ for endothermic reactions?

Answer: $K_c$ increases with an increase in temperature. Higher temperature favors endothermic reactions, increasing $K_c$.