Reaction Quotient Calculator (Qc and Qp)

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Use Qc for reactions in solution or when given molar concentrations. Use Qp for gas-phase reactions when given partial pressures in atm. Both use the same mass-action formula; the units of the activities differ.
Loads example concentrations and coefficients so you can explore Q vs K right away.
Comma-separated values for each product species, in mol/L for Qc or atm for Qp, in the same order as the coefficients below. Pure solids and pure liquids are omitted (activity = 1).
Comma-separated stoichiometric coefficients of each product from the balanced equation. These become the exponents in the mass-action expression.
Comma-separated values for each reactant species, in mol/L for Qc or atm for Qp, in the same order as the coefficients below. Omit pure solids and liquids.
Comma-separated stoichiometric coefficients of each reactant from the balanced equation.
Supply K to see the Q vs K comparison and shift direction. Leave blank if you only need the value of Q. Match the type: Kc with Qc inputs, Kp with Qp inputs.
Useful when Q spans many orders of magnitude (very large or very small K). The log scale compresses the range and matches how Gibbs energy is expressed: DeltaG = RT ln Q/K.
Reaction quotient QShifts reverse
0.64

The mass-action ratio computed from the concentrations or pressures you entered.

Q (numeric)0.64
Q / K ratio1.28
Predicted shiftQ > K: shifts reverse (toward reactants)
Gibbs energy signDeltaG > 0: reverse reaction is spontaneous
1.28 Q/K
Far forward<0.5Shifts forward0.5-0.999Equilibrium0.999-1.001Shifts reverse1.001-1.8Far reverse1.8+

Your reaction quotient is Qc = 0.64.

  • Qc uses the same mass-action formula as K, with every product concentration (or pressure) raised to its coefficient in the numerator and every reactant in the denominator, computed at the instant you measured your mixture, not at equilibrium.
  • When Q equals K the forward and reverse rates are balanced and no net change occurs, even though both reactions continue at the molecular level.
  • For this mixture: Q > K: shifts reverse (toward reactants).
  • Gibbs perspective: DeltaG > 0: reverse reaction is spontaneous.

Next stepCompare to a Kc from a thermodynamic table or your equilibrium calculator to predict the shift direction.

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