Gibbs Free Energy Calculator
Calculate Gibbs free energy change (ΔG) and determine if a reaction is spontaneous. Uses ΔG = ΔH - TΔS, ΔG = -RT ln(K), or ΔG = -nFE.
Select the type of calculation
Enthalpy change in kJ/mol
Entropy change in J/mol·K (will be converted to kJ/mol·K)
Temperature in Kelvin
Equilibrium constant at temperature T
Cell electromotive force in Volts
Electrons transferred in the reaction
What is Gibbs free energy?
Gibbs free energy (G) measures the maximum useful work obtainable from a spontaneous process atconstant T and P. ΔG < 0 = spontaneous; ΔG > 0 = nonspontaneous; ΔG = 0 = equilibrium. The fundamental equation: ΔG = ΔH - TΔS.
How do you calculate ΔG?
Method 1: ΔG = ΔH - TΔS directly. Method 2: ΔG = -RT ln(K). Method 3: ΔG = -nFE (electrochemistry). All give identical results whenconditions are consistent. At 298 K: ΔG° = -RT ln(K) ≈ -5.708 log(K) kJ/mol.
What does ΔG determine?
ΔG determines spontaneity and equilibrium position. ΔG < 0: forward reaction favored. ΔG > 0: reverse favored. At equilibrium: ΔG = 0. The relationship: ΔG = ΔG° + RT ln(Q), where Q is the reaction quotient. This determines how far from equilibrium the system is.
What is the relationship between ΔG and K?
ΔG° = -RT ln(K). A 10-fold increase in K decreases ΔG° by ~5.71 kJ/mol at 298 K. For K = 1: ΔG° = 0 (equilibrium). K > 1: ΔG° < 0 (spontaneous products). K < 1: ΔG° > 0 (spontaneous reactants).
How does temperature affect ΔG?
Temperature directly affects ΔG through the -TΔS term. For exothermic + increase in entropy (ΔH < 0, ΔS > 0): always spontaneous. For endothermic + decrease in entropy: never spontaneous. Mixed signs: product-favored at either high or low temperature.