Gibbs Free Energy Calculator

Calculate ΔG and reaction spontaneity

Enter enthalpy, entropy, temperature, or equilibrium constant to compute Gibbs free energy and determine if a reaction is spontaneous.

Examples

See how to use the Gibbs Free Energy Calculator with real-world scenarios.

Spontaneous Reaction at Room Temperature

ΔG = ΔH - TΔS (Enthalpy, Entropy, Temperature)

Calculate ΔG for a reaction with ΔH = -40 kJ/mol, ΔS = -100 J/(mol·K), T = 25°C.

Calculation Type: hts

Enthalpy Change (ΔH): -40 kJ/mol

ΔH Unit: kJ/mol

Entropy Change (ΔS): -100 J/(mol·K)

ΔS Unit: J/(mol·K)

Temperature (T): 25 °C

Temperature Unit: °C

Non-Spontaneous at High Temperature

ΔG = ΔH - TΔS (Enthalpy, Entropy, Temperature)

Calculate ΔG for ΔH = 10 kJ/mol, ΔS = 50 J/(mol·K), T = 500 K.

Calculation Type: hts

Enthalpy Change (ΔH): 10 kJ/mol

ΔH Unit: kJ/mol

Entropy Change (ΔS): 50 J/(mol·K)

ΔS Unit: J/(mol·K)

Temperature (T): 500 K

Temperature Unit: K

Using Equilibrium Constant

ΔG = -RTlnK (Equilibrium Constant)

Calculate ΔG for K = 0.5 at 298 K.

Calculation Type: k

Temperature (T): 298 K

Temperature Unit: K

Equilibrium Constant (K): 0.5

Standard Conditions

ΔG = ΔH - TΔS (Enthalpy, Entropy, Temperature)

Calculate ΔG for ΔH = -285.8 kJ/mol, ΔS = -163.1 J/(mol·K), T = 25°C (formation of water).

Calculation Type: hts

Enthalpy Change (ΔH): -285.8 kJ/mol

ΔH Unit: kJ/mol

Entropy Change (ΔS): -163.1 J/(mol·K)

ΔS Unit: J/(mol·K)

Temperature (T): 25 °C

Temperature Unit: °C

Other Titles
Understanding Gibbs Free Energy: A Comprehensive Guide
Master the concept of Gibbs free energy and reaction spontaneity in chemistry.

What is Gibbs Free Energy?

  • Definition and Importance
  • Relation to Spontaneity
  • Units and Symbols
Gibbs free energy (ΔG) is a thermodynamic quantity that predicts whether a chemical reaction will occur spontaneously at constant pressure and temperature. It combines enthalpy, entropy, and temperature into a single value.
ΔG = ΔH - TΔS

Common Reactions

  • Combustion reactions
  • Photosynthesis

Step-by-Step Guide to Using the Calculator

  • Input Selection
  • Unit Consistency
  • Interpreting Results
Select the calculation type based on your available data: use enthalpy, entropy, and temperature, or the equilibrium constant. Ensure all units are compatible for accurate results.
How to Use the Calculator

Input Examples

  • ΔH in kJ/mol, ΔS in J/(mol·K), T in °C or K

Real-World Applications of Gibbs Free Energy

  • Predicting Reaction Spontaneity
  • Biological Systems
  • Industrial Chemistry
Gibbs free energy is used to predict if a reaction will proceed without external input. It is crucial in biochemistry, environmental science, and industrial processes.
Applications in Science and Industry

Application Examples

  • ATP hydrolysis in cells
  • Ammonia synthesis (Haber process)

Common Misconceptions and Correct Methods

  • ΔG and Reaction Rate
  • Unit Conversion Errors
  • Temperature Effects
A negative ΔG does not mean a reaction is fast, only that it is thermodynamically favorable. Always check unit consistency and convert temperature to Kelvin if needed.
Avoiding Calculation Mistakes

Mistake Examples

  • Mixing kJ and J units
  • Using °C instead of K

Mathematical Derivation and Examples

  • Derivation of ΔG Formulas
  • Sample Calculations
  • Interpreting ΔG Values
The formula ΔG = ΔH - TΔS is derived from the laws of thermodynamics. ΔG = -RTlnK links free energy to equilibrium. Sample calculations help understand the process.
Worked Examples

Calculation Examples

  • ΔG calculation for water formation
  • ΔG from equilibrium constant