Reaction Quotient Calculator
Compare the reaction quotient with the equilibrium constant to predict the direction of change.
About Reaction Quotient Calculator
When Q is below K the reaction moves forward; above K it reverses. The free energy change is RT ln (Q/K), which is zero exactly at equilibrium — the thermodynamic definition of the state. Q versus K is the fastest way to predict whether a mixture will react and in which direction, without solving the full equilibrium.
Formula
Reaction Quotient
Q has the same form as K but uses current concentrations; compare Q with K to find the direction
- Q
- Reaction quotient at the current, non-equilibrium composition
- ΔG
- RT ln(Q/K), zero at equilibrium
Worked example
With the default values below, Reaction Quotient Calculator returns Reaction Quotient of 0.600000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Product concentrationminimum 0 mol/L
- 0.3 mol/L
- Reactant concentrationminimum 0 mol/L
- 0.5 mol/L
- Equilibrium constantminimum 0
- 2
- Coefficient of the productaccepts 1–10
- 1
Results
- Reaction Quotient
- 0.600000
- Direction of Net Change
- Proceeds forward toward products
- Ratio of Q to K
- 0.300000
- Logarithmic Distance From Equilibrium
- -0.52288
- Free Energy Change Under These Conditions
- -2.9846 kJ/mol
Step by step
- 1Values used
- 2Reaction Quotient
- 3Reaction Quotient= 0.600000
- 4Direction of Net Change= Proceeds forward toward products
- 5Ratio of Q to K= 0.300000
- 6Logarithmic Distance From Equilibrium= -0.52288
- 7Free Energy Change Under These Conditions= -2.9846 kJ/mol
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Reaction Quotient calculated?
Q has the same form as K but uses current concentrations; compare Q with K to find the direction When Q is below K the reaction moves forward; above K it reverses. The free energy change is RT ln (Q/K), which is zero exactly at equilibrium — the thermodynamic definition of the state.
Why does Reaction Quotient matter?
Q versus K is the fastest way to predict whether a mixture will react and in which direction, without solving the full equilibrium.
What values do I need to enter?
This calculator takes 4 inputs: Product concentration, Reactant concentration, Equilibrium constant, Coefficient of the product. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.