# Gibbs Free Energy Calculator

Free Gibbs free energy calculator. Calculate ΔG, ΔH, ΔS, or temperature using ΔG = ΔH - TΔS. Determine reaction spontaneity.

## What this calculates

Calculate Gibbs free energy (ΔG) to determine whether a chemical reaction is spontaneous. Uses the fundamental equation ΔG = ΔH - TΔS, relating free energy to enthalpy, temperature, and entropy.

## Inputs

- **Solve For** — options: ΔG (Gibbs Free Energy), ΔH (Enthalpy Change), ΔS (Entropy Change), Temperature (T) — Select what to calculate.
- **ΔH (Enthalpy Change)** (kJ/mol) — Enthalpy change in kJ/mol. Negative = exothermic.
- **ΔS (Entropy Change)** (J/(mol·K)) — Entropy change in J/(mol·K). Note: J, not kJ.
- **Temperature** (K) — min 0 — Absolute temperature in Kelvin (K = °C + 273.15).
- **ΔG (Gibbs Free Energy)** (kJ/mol) — Gibbs free energy change in kJ/mol.

## Outputs

- **Result** — The calculated value.
- **Unit** — formatted as text — Unit of the result.
- **Spontaneity** — formatted as text — Whether the reaction is spontaneous.
- **Formula** — formatted as text — Step-by-step calculation.
- **Equilibrium Temperature** — formatted as text — Temperature where ΔG = 0 (if applicable).

## Frequently Asked Questions

**Q: What does Gibbs free energy tell us?**

A: Gibbs free energy (ΔG) predicts reaction spontaneity at constant temperature and pressure. ΔG < 0: spontaneous (exergonic). ΔG > 0: non-spontaneous (endergonic). ΔG = 0: at equilibrium.

**Q: Why are the units different for ΔH and ΔS?**

A: ΔH is typically in kJ/mol, while ΔS is in J/(mol·K). When using ΔG = ΔH - TΔS, you must convert to consistent units. This calculator converts ΔS from J to kJ by dividing by 1000.

**Q: What is the equilibrium temperature?**

A: The equilibrium temperature is where ΔG = 0, meaning ΔH = TΔS, so T = ΔH/ΔS. Above or below this temperature, the reaction may switch between spontaneous and non-spontaneous.

**Q: Can a reaction with positive ΔH be spontaneous?**

A: Yes, if ΔS is positive and large enough. At high temperatures, the TΔS term can overcome ΔH, making ΔG negative. Example: melting ice is endothermic but spontaneous above 0°C.

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Source: https://vastcalc.com/calculators/chemistry/gibbs-free-energy
Category: Chemistry
Last updated: 2026-04-21