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AP Chemistry Practice Quiz: Introduction to Le Châtelier’s Principle

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 9 questions to check your progress.

Question 1 of 9

According to Le Châtelier's principle, how does a system at equilibrium primarily respond to an external stress?

All Questions (9)

According to Le Châtelier's principle, how does a system at equilibrium primarily respond to an external stress?

A) It shifts in a direction that counteracts the stress.

B) The reaction rate increases in both directions equally.

C) The equilibrium constant (K) changes to a new value.

D) The reaction stops completely until the stress is removed.

Correct Answer: A

The core concept of Le Châtelier's principle is that a system at equilibrium, when subjected to a stress, will adjust itself to partially oppose or relieve the applied stress.

Which of the following is explicitly listed in the content as a type of stress that Le Châtelier's principle can be used to analyze?

A) Addition of a catalyst

B) Change in the shape of the reaction vessel

C) Change in temperature

D) Exposure to sunlight

Correct Answer: C

The provided content identifies several stresses, including the addition/removal of a species, change in temperature, change in volume/pressure, and dilution. A change in temperature is one of these specified stresses.

For a gas-phase system at equilibrium, a decrease in volume would be considered what type of stress?

A) A change in temperature

B) A change in pressure

C) A removal of a species

D) A dilution of the system

Correct Answer: B

The content states that Le Châtelier's principle applies to a 'change in volume/pressure of a gas-phase system'. For a gas, decreasing the volume directly increases the pressure, which is the stress the system will respond to.

If a chemical species is removed from a system at equilibrium, how will the system respond according to Le Châtelier's principle?

A) The equilibrium will shift to produce more of the removed species.

B) The equilibrium will shift to consume more of the removed species.

C) The temperature of the system will increase.

D) There will be no change in the equilibrium position.

Correct Answer: A

Le Châtelier's principle states the system will counteract the stress. The stress is the removal of a species, so the system will shift in the direction that replenishes or produces more of that species to partially restore its concentration.

The provided content states that Le Châtelier's principle can be used to predict the effect of a stress on certain measurable properties. Which of the following is one such property?

A) The activation energy of the reaction

B) The mass of the reactants

C) The color of a solution

D) The reaction mechanism pathway

Correct Answer: C

The content explicitly mentions that the principle can predict effects on experimentally measurable properties such as pH, temperature, and the color of a solution.

Consider an aqueous equilibrium where one of the products is a distinctively colored ion. If a reactant is added to this system, what is the most likely observable change based on Le Châtelier's principle?

A) The solution's color will fade or disappear.

B) The solution's color will become more intense.

C) The temperature of the solution will decrease.

D) The pH of the solution will remain constant.

Correct Answer: B

Adding a reactant is a stress. The system will shift to counteract this by consuming the added reactant, which means shifting the equilibrium towards the products. Since a product is the colored ion, producing more of it will make the solution's color more intense.

For an aqueous equilibrium that produces H⁺ ions as a product, what would be the predicted effect on the pH if a stress is applied that causes the equilibrium to shift toward the reactants?

A) The pH will decrease.

B) The pH will increase.

C) The pH will not change, but the temperature will.

D) The solution will become colorless.

Correct Answer: B

If the equilibrium shifts toward the reactants, the products (including H⁺ ions) will be consumed. A decrease in the concentration of H⁺ ions leads to a less acidic solution, which corresponds to an increase in pH.

A student is studying a gas-phase equilibrium in a container with a movable piston. If the student pulls the piston outwards, increasing the volume, what stress is being applied and how will the system respond?

A) The stress is an increase in temperature; the system will shift to absorb heat.

B) The stress is the addition of a product; the system will shift toward reactants.

C) The stress is a decrease in pressure; the system will shift to the side with more moles of gas.

D) The stress is dilution; the system will shift to the side with fewer moles of gas.

Correct Answer: C

Increasing the volume of a gas-phase system decreases its total pressure. According to Le Châtelier's principle, the system will respond to this stress by shifting in the direction that increases the pressure, which is the side of the reaction with the greater number of moles of gas.

Le Châtelier's principle can be used to predict the response of a system to all of the following stresses EXCEPT:

A) The addition of a product species.

B) The dilution of an aqueous system.

C) An increase in the system's temperature.

D) The addition of a catalyst to the system.

Correct Answer: D

The provided content lists addition/removal of a species, change in temperature, change in volume/pressure, and dilution as stresses. A catalyst increases the rate of both the forward and reverse reactions equally, allowing the system to reach equilibrium faster, but it does not cause a shift in the equilibrium position itself. Therefore, it is not considered a stress in the context of Le Châtelier's principle.