AP Chemistry Flashcards: Reaction Quotient and Le Châtelier’s Principle
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What is the relationship between the reaction quotient (Q) and the equilibrium constant (K) when a reversible reaction is at equilibrium?
When a reaction is at equilibrium, the reaction quotient (Q) is equal to the equilibrium constant (K).
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What is the relationship between the reaction quotient (Q) and the equilibrium constant (K) when a reversible reaction is at equilibrium?
When a reaction is at equilibrium, the reaction quotient (Q) is equal to the equilibrium constant (K).
What is the ultimate goal of the system's response after any stress is applied?
Regardless of the stress, the system's goal is to redistribute the concentrations of species to bring the reaction quotient (Q) and the equilibrium constant (K) back into equality.
After a temperature change establishes a new K value, how does the system reach its new equilibrium?
Following a temperature change, the species concentrations will redistribute, changing Q until it becomes equal to the new value of K.
How does a system that has been disturbed respond to re-establish equilibrium?
The system responds by shifting its concentrations to bring the value of Q back into agreement with K, thereby establishing a new equilibrium state.
What is the unique effect of a change in temperature on a system at equilibrium compared to other stresses?
Unlike other stresses that only affect Q, a change in temperature is the only disturbance that causes a change in the value of the equilibrium constant (K) itself.
Define 'stress' in the context of chemical equilibrium.
A stress is any disturbance to a system at equilibrium, such as a change in concentration or temperature, that causes Q to differ from K.
If Q < K, in which direction will a reversible reaction proceed to reach equilibrium?
If Q is less than K, the reaction will proceed in the forward direction (towards the products) to reach equilibrium.
According to Le Châtelier's Principle, what is the immediate effect of a disturbance on a system at equilibrium?
A disturbance to a system at equilibrium causes the reaction quotient (Q) to differ from the equilibrium constant (K), taking the system out of its equilibrium state.
When the concentration of a reactant or product is changed in a system at equilibrium, what value is directly affected: Q or K?
A change in the concentration of a species is a stress that causes a change in the reaction quotient (Q) only.
If Q > K, in which direction will a reversible reaction proceed to reach equilibrium?
If Q is greater than K, the reaction will proceed in the reverse direction (towards the reactants) to reach equilibrium.