Equilibrium Constant from ΔG

Compute the thermodynamic equilibrium constant (K) from Gibbs free energy change (ΔG°) for chemical reactions. Designed for students, researchers, and lab technicians. Works entirely offline in your browser. Accepts scientific notation (e.g., 1.23e-4).

Note: Educational only. Follow your lab SOPs and SDS.

Understanding K from ΔG°

The equilibrium constant (K) quantifies the position of equilibrium for a reaction at a given temperature. The fundamental link between thermodynamics and equilibrium is given by ΔG° = -RT ln K, where ΔG° is the standard Gibbs free energy change.

Step-by-Step Usage

Select calculation direction: ΔG° → K (most common) or K → ΔG°.
Enter your known values with appropriate units. Use scientific notation for very large/small numbers.
Ensure temperature is in a sensible range (typically 200–500 K for common reactions).
Click "Calculate". Review the intermediate value (-ΔG°/RT) for sanity.
Use "Copy Result" to log the value in your lab notebook.

Realistic Examples

Scenario	ΔG°	T	K (Result)	Interpretation
Weak acid dissociation	+27.1 kJ/mol	298.15 K	1.8 × 10^-5	Typical K_a for acetic acid
Highly favorable reaction	-50.0 kJ/mol	300 K	2.24 × 10⁸	Essentially goes to completion
Near-equilibrium	-1.0 kJ/mol	400 K	1.33	Reactants and products comparable

Common Mistakes Checklist

Using ΔG (non‑standard) instead of ΔG° (standard state).
Forgetting to convert ΔG units to J/mol before calculation.
Using Celsius or Fahrenheit temperature without conversion to Kelvin.
Interpreting K > 1 as "spontaneous" (spontaneity depends on ΔG, not K alone).
Applying the equation to non‑ideal systems (high ionic strength, non‑ideal gases) without activity corrections.

Equilibrium Constant from ΔG

Results

Primary Result

Intermediate Value

Quality Check

Understanding K from ΔG°

Step-by-Step Usage

Realistic Examples

Common Mistakes Checklist

Temperature Sensitivity

Frequently Asked Questions

What are the accuracy limits?

When does this approximation fail?

What unit pitfalls should I avoid?

Any measurement tips?

Formulas & Assumptions

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Equilibrium Constant from DeltaG

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