Measure reaction status with flexible stoichiometric inputs. View Q, compare K, and interpret direction instantly. Clean outputs, graphs, and exports support dependable equilibrium analysis.
Enter only species that belong in the reaction quotient expression. Leave pure solids and pure liquids blank when their activity is effectively one.
Sample reaction: N2 + 3H2 ⇌ 2NH3, using concentration terms.
| Species | Side | Coefficient | Concentration | Included in Q |
|---|---|---|---|---|
| N2 | Reactant | 1 | 0.30 | Yes |
| H2 | Reactant | 3 | 1.20 | Yes |
| NH3 | Product | 2 | 0.80 | Yes |
Example result: Qc = [NH3]2 / ([N2][H2]3) = 59.2593
General reaction form
aA + bB ⇌ cC + dD
Reaction quotient
Q = (activity of products raised to their coefficients) ÷ (activity of reactants raised to their coefficients)
Common working forms
Qc = [C]c[D]d / [A]a[B]b
Qp = PCcPDd / PAaPBb
Direction test with K
If Q < K, the reaction tends toward products.
If Q > K, the reaction tends toward reactants.
If Q ≈ K, the system is near equilibrium.
Thermodynamic relation
ΔG° = −RT ln(K)
ΔG = RT ln(Q/K)
Q measures the current ratio of product activities to reactant activities, each raised to their stoichiometric coefficients. It describes the reaction state at any moment, not only at equilibrium.
Q uses present conditions, while K is the equilibrium ratio at a given temperature. Comparing them shows whether the system will move forward, reverse, or remain close to equilibrium.
Usually no. Their activities are commonly treated as one, so they do not appear in the reaction quotient expression. Include only species whose activities vary meaningfully in the system.
Yes. Select the pressure mode to treat the entered values as partial pressures and compute Qp. Use consistent units for all gaseous species before interpreting the result.
The calculator uses powers and logarithms. Zero or negative entries make those thermodynamic calculations invalid or undefined. Positive values keep Q, ln(Q), and ΔG expressions mathematically meaningful.
When Q matches K within a small tolerance, the system is effectively at equilibrium for the chosen temperature. Under that condition, there is no net driving force in either direction.
Temperature is needed when converting the Q and K comparison into free energy terms. Without temperature, the calculator can still compute Q and direction, but not ΔG values.
The graph displays each species contribution to ln(Q). Product terms push ln(Q) upward, while reactant terms reduce it. This helps explain why the final quotient is large or small.
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.