Equilibrium constant calculator explained
For a general reaction , the equilibrium constant is . This calculator lets you enter stoichiometric coefficients ({corf_1}, {corf_2}, {copf_1}, {copf_2}) and molar concentrations ({cor_1}, {cor_2}, {cop_1}, {cop_2}) to evaluate instantly or solve for an unknown concentration that satisfies a reported K.
Use it while checking ICE-table work, validating simulation results, or turning spectroscopic concentration data into equilibrium constants for publication.
How the conversion works
The mass-action expression is:
where terms are stoichiometric coefficients. Gases can be handled with partial pressures () as long as you keep units consistent. The calculator raises each concentration to its coefficient and performs the ratio automatically.
Units and conversions
| Quantity | Meaning | Notes |
|---|---|---|
| Concentrations or activities | Use mol/L for , bar for , or activities for dimensionless K. | |
| Stoichiometric coefficients | Integers from the balanced equation. | |
| Equilibrium constant | Dimensionless when activities are used; otherwise carries units implied by concentrations. |
Worked examples
- at 298 K
, . Coefficients: , .
The value (0.11) matches handbook data within rounding.
at 731 K. If at equilibrium, solve for .
Enter the known concentrations and coefficients, and the calculator reports confirming the algebra.
Tips and pitfalls
- Only species in solution or gas phase appear in ; pure solids and liquids drop out because their activities equal 1.
- Keep units consistent—mixing mol/L and mmol/L produces incorrect K values.
- When converting between and , use with in kelvin and L atm mol K.
- Use logarithms (\(\log K\)) when handling very large or small constants to avoid floating-point overflow in spreadsheets.