Enter your reactant and product coefficients and their concentrations or pressures into this Reaction Quotient (Q) Calculator to find the reaction quotient (Q) and, if you provide the equilibrium constant (K), see the Q/K ratio and which direction the reaction will shift to reach equilibrium.
Reaction Quotient (Q)
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Reaction Direction
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Q/K Ratio
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The reaction quotient (Q) is a measure of the relative amounts of products and reactants present during a reaction at any point in time. It uses the same expression as the equilibrium constant but can be calculated for any set of conditions, not just at equilibrium.
For the general reaction aA + bB ⇌ cC + dD, Q = [C]^c × [D]^d / [A]^a × [B]^b. Substitute the actual concentrations (for Qc) or partial pressures (for Qp) and their stoichiometric coefficients into this expression.
Q is the reaction quotient calculated at any point during a reaction, while K is the equilibrium constant calculated only when the reaction is at equilibrium. Comparing Q to K tells us which direction the reaction will proceed.
If Q < K, the reaction proceeds forward (toward products). If Q > K, the reaction proceeds backward (toward reactants). If Q = K, the reaction is at equilibrium and no net change occurs.
Qc uses molar concentrations (mol/L) in the calculation, while Qp uses partial pressures (atm). Use Qc for reactions in solution and Qp for gas-phase reactions.
Use this calculator when you need to predict which way a chemical reaction will proceed from its current state, determine if a reaction mixture is at equilibrium, or understand the driving force behind a chemical reaction.
Yes, Q can be greater than K. When Q > K, it means there are too many products relative to reactants compared to the equilibrium state, so the reaction will shift backward to form more reactants.
The units of Q depend on the stoichiometry of the reaction. For many reactions, Q is dimensionless, but it can have units of concentration or pressure raised to various powers based on the balanced equation.