Thermodynamic Equilibrium Calculator for Chemistry Reactions

Enter Thermodynamic Inputs

Use reaction-standard values and a positive reaction quotient. Activities may represent normalized concentrations, fugacities, or partial pressures.

Analysis temperature, T (K)

Target temperature, T₂ (K)

Standard enthalpy change, ΔH° (kJ/mol)

Standard entropy change, ΔS° (J/mol·K)

Reaction quotient, Q

Reactant coefficient, ν_R

Product coefficient, ν_P

Initial reactant activity, a_R,0

Initial product activity, a_P,0

Example Data Table

Scenario	T (K)	T₂ (K)	ΔH° (kJ/mol)	ΔS° (J/mol·K)	Q	νR	νP	aR,0	aP,0
Sample exothermic equilibrium	500	650	-92.2	-198	0.20	1	2	1.50	0.10
Moderate endothermic system	700	900	45.0	72.0	3.50	1	1	2.00	0.60
Near-balanced free energy case	298.15	350	-15.0	-48.0	1.10	2	1	1.00	0.30

Formula Used

1. Standard Gibbs free energy
ΔG° = ΔH° − TΔS°

2. Equilibrium constant from free energy
K = exp(−ΔG° / RT)

3. Nonstandard Gibbs free energy
ΔG = ΔG° + RT ln(Q)

4. Temperature effect from van’t Hoff relation
ln(K₂ / K₁) = −ΔH°/R × (1/T₂ − 1/T₁)

5. Simplified one-reactant one-product equilibrium model
Q_eq = a_P^νP / a_R^νR

6. Activity balance with extent
a_R = a_R,0 − νRξ and a_P = a_P,0 + νPξ

The calculator applies these relations using SI-consistent energy units. ΔH° is entered in kJ/mol, ΔS° in J/mol·K, and the gas constant is 8.314462618 J/mol·K.

How to Use This Calculator

Enter the main analysis temperature in kelvin.
Enter a second temperature to study equilibrium temperature sensitivity.
Provide standard enthalpy and entropy changes for the reaction.
Enter the current reaction quotient Q for the present mixture.
Supply simple stoichiometric coefficients for one reactant and one product.
Enter initial normalized activities for the reactant and product.
Click Calculate Equilibrium to show results above the form.
Use the CSV and PDF buttons to export the current result set.

Frequently Asked Questions

1. What does this calculator estimate?

It estimates standard Gibbs energy, equilibrium constants, temperature-shifted constants, nonstandard Gibbs energy, and a simplified equilibrium composition using an extent balance.

2. Why is temperature entered twice?

The first temperature evaluates the present state. The second temperature predicts how equilibrium changes when the system is heated or cooled.

3. What is the meaning of Q?

Q is the current reaction quotient. Comparing Q with K shows whether the mixture must shift toward reactants or products to reach equilibrium.

4. Why can K become extremely large or tiny?

Because K depends exponentially on −ΔG°/RT. Small free-energy changes can create very large equilibrium differences, especially at lower temperatures.

5. Are activities the same as concentrations?

Not always. Activities are idealized effective quantities. For diluted or ideal systems, concentrations or partial pressures may approximate activities reasonably well.

6. Does this handle multi-species reactions exactly?

The energy and equilibrium-constant parts are general. The composition solver is simplified to one reactant and one product activity expression for practical estimation.

7. When is the temperature prediction most reliable?

It is most reliable when ΔH° and ΔS° stay nearly constant over the temperature interval and nonideal behavior remains limited.

8. Can I use these results for lab reporting?

Yes, for educational and preliminary analysis. For rigorous reporting, confirm assumptions, units, and activity models with your reaction system.