Reaction Quotient (Q) Calculator to Predict Reac...

What is the Reaction Quotient Q?

The reaction quotient (Q) has the same mathematical form as the equilibrium constant (K) but uses current concentrations rather than equilibrium concentrations. Comparing Q to K tells you whether a reaction needs to proceed forward, backward, or is already at equilibrium.

⚗️ Reaction Quotient Calculator

Use our free calculator for instant, accurate results.

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📐 Formula

Qc = [products]^n / [reactants]^m (current concentrations)

Same expression as Kc, but evaluated at any point in time. Compare to K: QK → reverse; Q=K → equilibrium.

📝 Worked Example

For N₂ + 3H₂ ⇌ 2NH₃, Kc = 0.5 at 500°C.
Current: [N₂]=0.1M, [H₂]=0.2M, [NH₃]=0.3M
Qc = 0.3² / (0.1 × 0.2³) = 0.09/0.0008 = 112.5
Qc (112.5) > K (0.5) → reaction shifts backward (toward reactants)

📝 How to Use the Calculator

Enter Current ConcentrationsInput [concentrations] in mol/L for all species right now.

Enter K ValueEquilibrium constant at the current temperature.

Calculate QView Qc (concentration) or Qp (pressure) and compare to K.

Predict DirectionSee which direction the reaction will shift to reach equilibrium.

❓ FAQ

Can Q be used with partial pressures?

Yes — Qp uses partial pressures (atm or bar) instead of concentrations. It equals Kp at equilibrium.

How does Q help in industrial chemistry?

Engineers monitor Q to ensure reactors operate efficiently without exceeding equilibrium, and to decide when to remove products to drive reactions forward.