Reaction Quotient Calculator
Calculate the reaction quotient Q for a chemical reaction from the activities or concentrations of reactants and products. This page supports up to six reactants and six products, each with its own stoichiometric coefficient.
Reactants
Products
Reaction Quotient
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Quick Answer: The reaction quotient uses the same algebraic form as an equilibrium constant: Q = product(a_product^coefficient) / product(a_reactant^coefficient). The difference is that Q uses the current activities, not necessarily equilibrium values.
How to Calculate the Reaction Quotient
- Enter reactant coefficients and activities: Fill only the rows you need for the balanced reaction.
- Enter product coefficients and activities: Use the same activity basis across the whole calculation.
- Choose precision: The result can be rounded from 0 to 6 decimal places.
- Interpret Q: Q greater than 1 means the current mixture is product-heavy, while Q less than 1 means it is reactant-heavy.
Reaction Quotient Calculator Formula
Q = product(products activities^coefficients) / product(reactants activities^coefficients)
| Variable | Meaning | Unit |
|---|---|---|
| Q | Reaction quotient | unitless in the simplified treatment |
| a | Activity or concentration term | activity basis used in the calculation |
| Coefficient | Stoichiometric exponent from the balanced equation | unitless |
Worked Examples
Example 1 - H2 + I2 <-> 2HI
- Reactants: [H2] = 0.20, [I2] = 0.20
- Products: [HI] = 0.80
- Coefficients: 1, 1, 2
Result: Q = 16.00
The current mixture is strongly product-heavy because the numerator dominates the expression.
Example 2 - N2 + 3H2 <-> 2NH3
- Reactants: [N2] = 0.50, [H2] = 0.50
- Products: [NH3] = 0.40
- Coefficients: 1, 3, 2
Result: Q = 2.56
Q is above 1, so the composition currently favors products more than reactants.
Example 3 - A + B <-> C
- Reactants: [A] = 0.90, [B] = 0.60
- Products: [C] = 0.12
- Coefficients: 1, 1, 1
Result: Q = 0.2222
Because Q is below 1, the mixture is reactant-heavy at the moment you sampled it.
Q Interpretation Table
| Range | Meaning | Action |
|---|---|---|
| Q < 1 | The present mixture is relatively rich in reactants. | If you later compare Q with K, the reaction may still tend toward products. |
| Q = 1 | Reactant and product terms balance to a quotient of one. | This does not by itself prove equilibrium unless K is also 1. |
| Q > 1 | The present mixture is relatively rich in products. | If you later compare Q with K, the reaction may tend toward reactants. |
Frequently Asked Questions
The reaction quotient Q is the current ratio of product activities to reactant activities, each raised to the coefficients from the balanced reaction.
Q is calculated from the present mixture, while K is the equilibrium constant for the reaction at a given temperature.
They come directly from the balanced chemical equation and define how each species contributes to the quotient.
For many classroom problems, concentrations are used as a practical approximation to activities.
It means the current mixture is product-heavy. To know the spontaneous direction, you still need to compare Q with K.
Note: This calculator reports Q from the values you enter. It does not determine equilibrium direction by itself unless you also compare the result with K.
References
Last reviewed: March 14, 2026