AP Chemistry Flashcards: Calculating Equilibrium Concentrations
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.
How is the equilibrium constant (K) used to predict the final state of a reaction?
The equilibrium constant (K) defines the specific ratio of product concentrations to reactant concentrations that must be reached for a system to be at equilibrium.
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How is the equilibrium constant (K) used to predict the final state of a reaction?
The equilibrium constant (K) defines the specific ratio of product concentrations to reactant concentrations that must be reached for a system to be at equilibrium.
What three pieces of information are necessary to predict the concentrations of species at equilibrium?
To predict equilibrium concentrations, you need the balanced chemical reaction, the initial concentrations or partial pressures, and the appropriate equilibrium constant (K).
What is the state of a system when the reaction quotient (Q) is equal to the equilibrium constant (K)?
When Q = K, the system is at dynamic equilibrium, where the rates of the forward and reverse reactions are equal and net concentration changes cease.
A system's concentrations are measured and Q is calculated to be 2.5. The equilibrium constant (K) for the reaction is 5.0. What will happen to the reactant concentrations?
Since Q < K (2.5 < 5.0), the reaction will proceed in the forward direction. This will cause the reactant concentrations to decrease as they are consumed to form more products.
If a chemist mixes products and reactants, and the reaction begins to form more reactants, what can be concluded about the initial state of the system?
It can be concluded that the initial reaction quotient (Q) was greater than the equilibrium constant (K), causing the reaction to proceed in the reverse direction.
Dynamic Equilibrium
A state in which the rate of the forward reaction is equal to the rate of the reverse reaction, represented by the condition Q = K.
What is the primary objective when calculating equilibrium concentrations?
The objective is to identify the concentrations or partial pressures of chemical species at equilibrium, based on the initial conditions and the equilibrium constant.
What does the condition Q < K indicate about a chemical reaction?
When Q < K, the ratio of products to reactants is less than it is at equilibrium, so the reaction will proceed in the forward direction, consuming reactants and forming products.
A reaction is initiated with only reactants present. What is the initial relationship between Q and K, and which way will the reaction proceed?
Initially, Q will be less than K (Q=0 if no products are present). The reaction will proceed in the forward direction, forming products.
If Q > K for a system, in which direction will the reaction shift to reach equilibrium?
When Q > K, the ratio of products to reactants is greater than at equilibrium, so the reaction will proceed in the reverse direction, consuming products and forming reactants.