Gibbs Free Energy Calculator

Calculate Gibbs free energy change from enthalpy, entropy, and temperature using the thermodynamic relationship ΔG = ΔH − TΔS.

Instant Result °C & Kelvin Thermodynamics Tool

Calculate Gibbs Free Energy

Enter enthalpy change, entropy change, and temperature.

Formula: ΔG = ΔH − TΔS. The calculator automatically converts temperature to Kelvin and makes the entropy units compatible with enthalpy units.

Enthalpy Change (ΔH)

Positive or negative values are accepted.

Entropy Change (ΔS)

Entropy will be converted to kJ/(mol·K).

Temperature (T)

Temperature is converted to absolute temperature.

Result Unit Choose the preferred unit for ΔG.

Gibbs Free Energy Equation
ΔG = ΔH − TΔS
T must be expressed as absolute temperature.

Gibbs Free Energy Change (ΔG)

kJ/mol

ΔH -

T -

ΔS -

Thermodynamics Guide

What Is Gibbs Free Energy?

Gibbs free energy is a thermodynamic quantity used to describe the energy change associated with a process. At constant temperature and pressure, the sign of the Gibbs free energy change helps determine the thermodynamic direction of a process.

Gibbs free energy combines enthalpy and entropy effects. This makes it useful for studying chemical reactions, phase changes, equilibrium, and many other thermodynamic processes.

Main Formula

Gibbs Free Energy Formula

When temperature is constant, Gibbs free energy change can be calculated from the enthalpy change, entropy change, and absolute temperature.

ΔG = ΔH − TΔS ΔG = Gibbs Free Energy Change • ΔH = Enthalpy Change • T = Temperature in Kelvin • ΔS = Entropy Change

How It Works

How to Use the Gibbs Free Energy Calculator

Enter ΔH and ΔS

Enter the enthalpy change and entropy change, including their positive or negative signs.

Enter Temperature

Add the temperature in Celsius, Kelvin, or Fahrenheit. It will be converted to Kelvin automatically.

Calculate ΔG

Click calculate to find Gibbs free energy and view the thermodynamic interpretation of the result.

Result Interpretation

What Does the Sign of ΔG Mean?

ΔG < 0

A negative Gibbs free energy change indicates that the process is thermodynamically spontaneous in the forward direction under the specified conditions.

ΔG = 0

When Gibbs free energy change is zero, the system is at thermodynamic equilibrium under the specified conditions.

ΔG > 0

A positive Gibbs free energy change means the forward process is thermodynamically nonspontaneous under the specified conditions.

Worked Example

Gibbs Free Energy Calculation Example

Suppose a process has an enthalpy change of −100 kJ/mol, an entropy change of −150 J/(mol·K), and a temperature of 25°C.

First convert the temperature to 298.15 K and entropy to −0.150 kJ/(mol·K). Then substitute the values into the Gibbs free energy equation.

ΔG = −100 − [298.15 × (−0.150)] ΔG ≈ −55.28 kJ/mol

Formula Reference

Gibbs Free Energy Variables

Symbol	Meaning	Common Unit
ΔG	Gibbs Free Energy Change	kJ/mol
ΔH	Enthalpy Change	kJ/mol
T	Absolute Temperature	K
ΔS	Entropy Change	kJ/(mol·K) or J/(mol·K)

Understanding the Equation

How Temperature Affects Gibbs Free Energy

Temperature influences the entropy contribution, TΔS, in the Gibbs free energy equation. Therefore, changing temperature can change the value and, in some cases, the sign of ΔG.

ΔH	ΔS	General Temperature Effect
Negative	Positive	ΔG tends to remain negative
Positive	Negative	ΔG tends to remain positive
Negative	Negative	Lower temperatures may favor negative ΔG
Positive	Positive	Higher temperatures may favor negative ΔG

Important: A negative ΔG indicates thermodynamic favorability under the specified conditions, but it does not tell you how quickly a process will occur.

Frequently Asked Questions

Gibbs Free Energy Calculator FAQs

What is the formula for Gibbs free energy?

At constant temperature, Gibbs free energy change is commonly calculated using ΔG = ΔH − TΔS.

What does a negative ΔG mean?

A negative ΔG indicates that the process is thermodynamically spontaneous in the forward direction under the specified conditions.

What does a positive ΔG mean?

A positive ΔG indicates that the forward process is thermodynamically nonspontaneous under the specified conditions.

What happens when ΔG equals zero?

When ΔG is zero, the system is at equilibrium under the specified conditions.

Why is temperature converted to Kelvin?

Thermodynamic equations involving absolute temperature require temperature in Kelvin. The calculator therefore converts Celsius or Fahrenheit automatically.

Can entropy be entered in J/(mol·K)?

Yes. You can enter entropy in J/(mol·K) or kJ/(mol·K). The calculator automatically converts the value before calculating ΔG.

Does negative ΔG mean a reaction is fast?

No. Gibbs free energy describes thermodynamic favorability, not reaction rate. Kinetics and activation barriers determine how quickly a reaction proceeds.

Can temperature change the sign of ΔG?

Yes. Because temperature multiplies the entropy term in ΔG = ΔH − TΔS, changing temperature can change the value and sometimes the sign of Gibbs free energy.