What is the reaction quotient Q?

Q is calculated from the concentrations of products and reactants at any given moment using the same formula as Keq: Q = [products]^coeff / [reactants]^coeff. Unlike Keq, Q can be evaluated before equilibrium is reached.

What does it mean when Q < Keq?

When Q is less than Keq, the reaction has fewer products (or more reactants) than at equilibrium. The reaction will proceed forward (left to right) to reach equilibrium.

What does it mean when Q > Keq?

When Q is greater than Keq, the reaction has too many products relative to equilibrium. The reaction will shift in reverse (right to left) to reach equilibrium.

What does it mean when Q = Keq?

The system is at equilibrium. No net change in concentrations occurs, and forward and reverse reaction rates are equal.

Are pure solids and liquids included in Q?

No. Pure solids and liquids have constant activity (= 1) and are excluded from the Q expression, just as they are from Keq. Only aqueous and gas-phase species with variable concentrations are included.

What units should I use for concentration?

Enter molar concentrations in mol/L (M). For gas-phase reactions, partial pressures in atm can be used instead, giving Qp rather than Qc.

Reaction Quotient Calculator

Enter reactant and product concentrations with stoichiometric coefficients to calculate Q and compare it to Keq.

Reactants

Products

Equilibrium Constant K_eq (optional — leave blank to skip comparison)

Enter concentrations and click "Calculate Q"

Summary

The reaction quotient (Q) measures the relative amounts of products and reactants at any point in a chemical reaction, using the same expression as the equilibrium constant (Keq). By comparing Q to Keq you can predict whether the reaction will shift forward (toward products), shift in reverse (toward reactants), or is already at equilibrium. This calculator supports up to four reactants and four products, each with their own concentration and stoichiometric coefficient.

How it works

Enter the stoichiometric coefficient and molar concentration for each reactant.
Enter the stoichiometric coefficient and molar concentration for each product.
Add up to four reactants and four products using the "Add" buttons.
Click "Calculate Q" to compute the reaction quotient.
The tool compares Q with your entered Keq and states the reaction direction.

Use cases

Determine whether a reaction has reached equilibrium or which way it will shift.
Verify lab measurements against the expected equilibrium constant.
Solve general-chemistry and AP Chemistry equilibrium problems.
Check ICE table setups by computing Q before any shifts occur.
Compare Q to Keq to predict product yield in industrial processes.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu