equilibrium constant formulas and interpretation
The thermodynamic equilibrium constant is related exponentially to standard Gibbs free energy.
The equation-based interface retains its built-in substance data and accepts custom thermodynamic values.
How to use the equilibrium constant calculator
- Choose a model: Select the relationship matching the problem.
- Choose the unknown: Select the quantity to calculate.
- Enter values: Enter all known values with matching units and signs.
- Calculate: Review the result, formula, units, and direction.
Formula and variables
The equilibrium constant equals the exponential of negative standard Gibbs energy divided by RT.
K = exp(−ΔG°/RT)- K — Equilibrium constant
- Dimensionless thermodynamic equilibrium constant (dimensionless)
- ΔG° — Standard Gibbs energy
- Standard reaction free-energy change (J/mol)
- R — Gas constant
- Molar gas constant (J/(mol·K))
- T — Temperature
- Absolute temperature (K)
Free-energy example
Use ΔG° = −5.00 kJ/mol at 298.15 K.
- ΔG°
- −5000 J/mol
- Temperature
- 298.15 K
- K = exp(5000/(8.314×298.15))
Result: K is approximately 7.52.
Under the selected standard-state convention, products are favored relative to reactants.
Understanding your results
Interpreting the result
K greater than one favors products, while K below one favors reactants; it does not indicate reaction speed.
Assumptions
- The selected equation represents the physical system.
- Inputs use a consistent reference direction.
- Values are converted through coherent SI units.
Limitations
- Vector components must be resolved along a common axis.
- External forces or energy losses are not added automatically.
- Results depend on the accuracy of entered measurements.
Common mistakes
- Mixing incompatible units.
- Dropping negative signs that represent direction.
- Using weight where mass is required.
- Entering a zero divisor.
Practical use cases
Physics problems
Check classroom, laboratory, and mechanics calculations.
Practical estimates
Estimate motion, forces, and energy for real systems.
Frequently asked questions
Can a result be negative?
Yes. For directional quantities, the sign indicates direction relative to the chosen positive axis.
Should I use SI units?
The interface can convert supported units, while the formulas are evaluated through coherent SI units.
Sources and review
- SI Brochure, 9th edition — BIPM. Accessed 2026-07-11.
- Special Publication 811 — NIST. Accessed 2026-07-11.
Reviewed 2026-07-11.