Model mixtures, gases, and solutions with confidence. Build Q from concentrations, pressures, or activities easily. Compare with K to predict which way equilibrium moves.
| Role | Species | ν | Value |
|---|---|---|---|
| Reactant | N2 | 1 | 0.80 |
| Reactant | H2 | 3 | 0.25 |
| Product | NH3 | 2 | 0.60 |
| For N2 + 3H2 → 2NH3, Q = (0.602) / (0.80 × 0.253). | |||
| Time | Basis | Equation | Q | K | Note |
|---|---|---|---|---|---|
| No saved calculations yet. | |||||
Q summarizes current mixture composition at the moment you sample it. In batch work, Q typically drifts as reactants are consumed and products accumulate. Tracking Q alongside time helps validate mixing, sampling, and analytical repeatability. A stable Q trend often indicates steady conditions, while oscillations can signal measurement noise or temperature fluctuations.
This calculator accepts species, stoichiometric coefficient ν, and an activity-like value. For solutions, values are commonly molar concentrations; for gases, partial pressures are typical. Each ν becomes an exponent, so a small coefficient error can shift Q substantially. For example, doubling ν doubles the log contribution of that species.
When you provide K, the tool compares Q and K to infer the favored shift. If Q < K, products are underrepresented, so the reaction tends to move forward. If Q > K, products are overrepresented, so the system tends to move backward. When Q ≈ K, the mixture is near equilibrium. For heterogeneous systems, omit pure solids and liquids by setting their activity to 1. Always record temperature, because K changes with temperature and can alter your interpretation even when composition is unchanged from run to next.
Many equilibria produce very small or very large Q values. Internally, the calculator uses logarithms to combine terms as Σν ln(a). This reduces overflow and preserves precision when activities span several orders of magnitude. It also clarifies which terms dominate, because the largest ν ln(a) contributions drive ln(Q).
Each submission is stored in session history and displayed in a table that exports to CSV and PDF. This is useful for lab notebooks, validation checklists, and quick comparisons between runs. Keeping a short rolling window encourages consistent naming and units across entries, improving interpretability of trends.
The Plotly graph visualizes Q values from your recent history. A rising curve can indicate increasing product activity, while a flat line may confirm a controlled equilibrium setup. If you also input K repeatedly, you can compare whether Q converges toward K across iterations, supporting troubleshooting and process optimization.
No. Q is calculated from the current composition, while K is fixed for a given reaction at a given temperature. Q can change as the system evolves.
For many equilibrium calculations, pure solids and pure liquids are treated as having activity 1 and are omitted from Q. If you include them, use value 1.
Yes. Choose the partial pressure basis and enter each species’ partial pressure. Keep units consistent across species, and use stoichiometric coefficients as exponents.
Q uses exponents and logarithms internally, which require positive values. If a species is effectively absent, use a small positive value consistent with your detection limit.
If Q is less than K, the system tends to form more products. If Q is greater than K, it tends to form more reactants. If Q is close to K, it is near equilibrium.
Yes. K depends strongly on temperature for many reactions. If your temperature changes, use a K value appropriate for that temperature before drawing conclusions from Q versus K.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.