Reaction Quotient Calculator
Evaluate Q to determine whether a mixture drifts toward products or reactants relative to equilibrium.
Reaction quotient Q
0.08333
How to Use This Calculator
Balance the reaction
Ensure the reaction is balanced and note each stoichiometric coefficient.
Enter concentrations or pressures
Provide the current mixture concentrations (mol/L) or partial pressures (atm).
Compute Q
Each value is raised to its coefficient and the product ratio is formed automatically.
Compare with K
Contrast Q with the equilibrium constant K to predict the shift direction.
Formula
Q = (products raised to their coefficients) / (reactants raised to their coefficients)
Q uses the same form as the equilibrium constant K, but the inputs reflect the current state rather than equilibrium.
Example
For N2 + 3H2 -> 2NH3 with [N2] = 0.20, [H2] = 0.30, [NH3] = 0.10 mol/L: Q = (0.10^2) / (0.20 × 0.30^3) ≈ 0.41.
Full Description
The reaction quotient Q provides a snapshot of how a reacting mixture compares with its equilibrium state. This calculator structures the classic expression for you: enter the stoichiometric coefficients, supply the current concentrations or partial pressures, and it raises each term to the appropriate power before forming the product-to-reactant ratio.
Visual feedback and validation make it simple to test multiple scenarios. Adjust a single concentration, recompute Q, and immediately see whether the mixture will shift toward products (Q < K) or reactants (Q > K). Because the expression mirrors the standard equilibrium constant form, you can copy the result straight into kinetics notes, lab reports, or reactor troubleshooting worksheets.
Ideal for
- General chemistry courses: Reinforce the conceptual link between Q and K.
- Process engineers: Diagnose whether a reactor is product- or reactant-heavy in real time.
- Research labs: Iterate through experimental concentrations without rebuilding spreadsheets.
Why it helps
- ✅ Flexible inputs: Accepts concentrations or partial pressures with scientific notation.
- ✅ Instant comparison: Pair the computed Q with a known K to predict direction of change.
- ✅ Error prevention: Ensures all species values are positive before building the expression.
- ✅ Reusable template: Balance any 2-to-2 reaction quickly without manual algebra.
Frequently Asked Questions
How do I handle solids or liquids?
Exclude pure solids and liquids, because their activities are approximately 1.
Can I use pressures instead of concentrations?
Yes. Use partial pressures for gas phase reactions and the same exponent rules apply.
Do units matter?
Q is dimensionless as long as you use consistent units across all species.
What if Q equals K?
The system is at equilibrium and no net change occurs.
Can I extend this to more species?
This template handles four species. Expand the expression manually if additional reactants or products are present.