Gibbs Free Energy & Equilibrium Calculator (ΔG = −RT ln K)
Explore the relationship between Gibbs free energy and equilibrium. Convert between ΔG° and K, and between ΔG and Q. See whether reactions are spontaneous or equilibrium-favored under given conditions.
Gibbs Free Energy & Equilibrium Calculator
Enter a temperature and at least one of ΔG°, K, ΔG, or Q to explore the relationships between Gibbs free energy and equilibrium.
ΔG° = −RT ln K
Connects standard Gibbs free energy to the equilibrium constant. When ΔG° < 0, K > 1 (products favored).
ΔG = ΔG° + RT ln Q
Connects current free energy to composition. When ΔG < 0, the forward reaction proceeds spontaneously.
Spontaneity
ΔG < 0: Forward reaction is spontaneous. ΔG > 0: Reverse reaction is spontaneous. ΔG = 0: At equilibrium.
Equilibrium Position
K ≫ 1: Products strongly favored. K ≪ 1: Reactants strongly favored. K ≈ 1: Significant amounts of both.
Note: K and Q should be treated as dimensionless activity ratios. This tool is for educational purposes only.
Understanding Gibbs Free Energy and Equilibrium
What is ΔG°?
The standard Gibbs free energy change (ΔG°) is the free energy change when all reactants and products are in their standard states at temperature T. It tells us which side is thermodynamically favored at equilibrium.
ΔG° < 0 → K > 1 (products favored)
ΔG° > 0 → K < 1 (reactants favored)
The ΔG° = −RT ln K Relationship
This fundamental equation connects thermodynamics (ΔG°) to equilibrium (K). A more negative ΔG° means a larger K and stronger preference for products at equilibrium.
K = e−ΔG°/RT
R = 8.314 J·mol⁻¹·K⁻¹ = 0.008314 kJ·mol⁻¹·K⁻¹
ΔG vs ΔG°: Current Conditions vs Standard State
While ΔG° tells us about equilibrium position, ΔG tells us whether a reaction will proceed spontaneously at thecurrent composition (described by Q).
ΔG < 0
Forward reaction is spontaneous. Q < K, so the system moves toward products.
ΔG = 0
System is at equilibrium. Q = K, no net change in concentrations.
ΔG > 0
Reverse reaction is spontaneous. Q > K, so the system moves toward reactants.
ΔG = ΔG° + RT ln Q = RT ln(Q/K)
When Q = K, ln(Q/K) = 0, so ΔG = 0 (equilibrium)
Key Concepts and Limitations
Dimensionless K and Q
Strictly speaking, K and Q are ratios of activities (effective concentrations). For ideal systems, we approximate activities with concentrations (mol/L) or partial pressures (bar or atm).
Temperature Dependence
Both ΔG° and K depend on temperature. This tool uses a fixed T. For different temperatures, you'd need the van 't Hoff equation or temperature-dependent ΔG° data.
Spontaneity ≠ Speed
A negative ΔG means a reaction can proceed, but says nothing about how fast. Kinetics (activation energy, catalysts) determines reaction rate.
Biochemical Standard States
Biochemistry often uses ΔG°′ (pH 7, 1 M concentrations, 1 atm). These values differ from standard thermodynamic tables. Always check which convention applies.
Educational Use Only: This calculator is for learning and conceptual understanding. Real-world applications require considering non-ideal behavior, activity coefficients, coupled reactions, and temperature effects. Do not use for industrial process design or safety-critical applications.
Frequently Asked Questions
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