Reaction Quotient Calculator

For a reaction aA + bB ↔ cC + dD, the concentration quotient is Q = [C]^c[D]^d ÷ ([A]^a[B]^b). Raise each product and reactant concentration to its stoichiometric coefficient, multiply the product terms together for the numerator and the reactant terms for the denominator, then divide. Pure solids and pure liquids are left out of the expression.

The reaction quotient Q uses the current concentrations at any moment, while the equilibrium constant K uses the concentrations at equilibrium. Comparing them shows which way the reaction will move.

When Q is smaller than K there are relatively too few products, so the reaction proceeds forward to make more products until Q rises to equal K.

No. Pure solids and pure liquids are left out of the reaction quotient expression because their activities are taken as one.

This calculator computes the concentration-based quotient Qc, so enter molar concentrations in mol/L. Gas-phase reactions are often described with the pressure-based quotient Qp built from partial pressures instead. Qc and Qp answer the same equilibrium question but are equal only when the number of moles of gas does not change across the reaction.