Chemistry
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Reaction Quotient Calculator.
Calculate Q from explicit product and reactant activities and stoichiometric coefficients.
Set your values
Results update as you type.
How to Use
Q = (aₚ₁^νₚ₁ × aₚ₂^νₚ₂) ÷ (aᵣ₁^νᵣ₁ × aᵣ₂^νᵣ₂). Activities and coefficients are explicit inputs.
Use a named source convention for coefficients and units. This page does not provide laboratory, medical, species, or food-safety advice.
Use Cases
Predict Reaction Direction
Determine whether a reaction will proceed forward or backward by comparing Q to the equilibrium constant K.
Example: For N2 + 3H2 ⇌ 2NH3, if Q < K, the reaction will produce more ammonia.
Check Equilibrium Status
Assess if a reaction mixture is at equilibrium by seeing if Q equals K.
Example: If Q = K, the system is at equilibrium and no net change occurs.
Frequently Asked Questions
- What is the reaction quotient Q?
- The reaction quotient Q is a measure of the relative amounts of products and reactants present during a reaction at a given moment. It is calculated using the same formula as the equilibrium constant K, but with concentrations or activities that are not necessarily at equilibrium.
- How do I use this calculator?
- Enter the activities (or concentrations) of each product and reactant, along with their stoichiometric coefficients from the balanced chemical equation. The calculator will compute Q by raising each activity to the power of its coefficient and dividing the product of product terms by the product of reactant terms.
- What is the difference between Q and K?
- Q is calculated at any point during a reaction, while K is the value of Q at equilibrium. Comparing Q to K tells you the direction the reaction will proceed: if Q < K, the reaction moves forward; if Q > K, it moves in reverse; if Q = K, the reaction is at equilibrium.
Tips & Common Mistakes
Tips
- Ensure the chemical equation is balanced before entering stoichiometric coefficients.
- Use activities for accurate results; for dilute solutions, molar concentrations are often used as approximations.
- Double-check that you enter the correct coefficient for each species, as it becomes the exponent in the Q expression.
- Remember that pure solids and liquids have an activity of 1 and are omitted from the Q expression.
Common Mistakes to Avoid
- Forgetting to raise each activity to the power of its stoichiometric coefficient.
- Reversing the numerator and denominator: products go on top, reactants on the bottom.
- Including pure solids or liquids in the expression, which should be omitted.
Last updated: August 13, 2026