Calculadora de Quociente de Reação
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
Q vs K: Q < K → direção direta ; Q > K → direção inversa
About this calculator
This calculator determines the reaction quotient (Q) for a generic chemical reaction of the form aA + bB ⇌ cC + dD. The reaction quotient is calculated using the expression Q = ([C]^c * [D]^d) / ([A]^a * [B]^b), where [A], [B], [C], [D] are the molar concentrations of reactants and products, and a, b, c, d are their stoichiometric coefficients. The tool compares Q with the equilibrium constant (K) to predict the direction in which the reaction will proceed to reach equilibrium.
The operation is simple: the user enters the molar concentrations of reactants and products, the stoichiometric coefficients, and the value of K. The calculator computes Q and compares it to K. If Q < K, the reaction proceeds forward (formation of products). If Q > K, the reaction proceeds backward (formation of reactants). If Q = K, the reaction is at equilibrium. This calculation is essential for predicting the behavior of chemical systems out of equilibrium.
Use this calculator in laboratories or chemistry studies to analyze reversible reactions, such as in industrial processes, compound synthesis, or reactions in solution. It is useful for students and professionals who need to quickly check whether a system is at equilibrium or which direction the reaction will take. For example, when mixing reactants in a reactor, knowing whether Q < K or Q > K helps adjust conditions to maximize yield.
Important precautions: ensure concentrations are in the same unit (usually mol/L) and that coefficients are correctly balanced. Remember that Q is calculated with current concentrations, not at equilibrium. The Q vs K comparison is only valid for homogeneous reactions at constant temperature, as K varies with temperature. Do not confuse Q with K: Q is instantaneous, K is constant for a given temperature.
Frequently asked questions
What does it mean when Q is less than K?
If Q < K, the reaction is not at equilibrium and will proceed forward, forming more products until Q equals K.
Can I use this calculator for gas-phase reactions?
Yes, as long as concentrations are in mol/L. For gases, partial pressures can be used instead of concentrations, with an analogous formula: Qp = (PC^c * PD^d) / (PA^a * PB^b).
What happens if I enter zero concentration for a reactant or product?
If any concentration is zero, the quotient Q becomes undefined (division by zero or zero in numerator). This indicates the reaction cannot proceed in that direction because a component is missing.
Does the calculator work for reactions with fractional coefficients?
Yes, coefficients can be decimals. The formula uses exponents, so enter coefficients as decimal numbers (e.g., 0.5).
What is the difference between Q and K?
Q is the reaction quotient at any instant, calculated with current concentrations. K is the equilibrium constant, which depends only on temperature. When Q = K, the system is at equilibrium.