Reaction Quotient - AP® Chemistry Definition

What is the reaction quotient?

The reaction quotient, denoted as Q, is a dimensionless number that provides a snapshot of a chemical reaction's progress at a particular point in time. It is calculated using the concentrations of reactants and products in a manner similar to the equilibrium constant, K, except the values are not necessarily at equilibrium.

For a given reaction at a specific temperature, the reaction quotient is determined by inserting the current concentrations or partial pressures into the expression for the equilibrium constant. Comparing Q to K allows students to predict the direction in which the reaction will proceed to attain equilibrium; if Q < K, the reaction shifts to the right (towards products), if Q > K, it shifts to the left (towards reactants), and if Q = K, the system is at equilibrium.

Understanding the reaction quotient is crucial for analysing chemical dynamics and predicting reaction behaviour in various conditions.

Reaction Quotient Revision Resources to Ace Your Exams

For more information about the reaction quotient check out the following resources:

• Reaction Quotient Study Guides

• Reaction Quotient & Le Chatelier's Principle Study Guides

• Equilibrium Exam Questions

Explore our AP Chemistry Revision Resources.