Equilibrium Constant Calculator Formula

Understand the math behind the equilibrium constant calculator. Each variable explained with a worked example.

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Formulas Used

Equilibrium Constant (K)

k_eq = pow(e, -(delta_g * 1000) / (8.314 * temp))

Variables

VariableDescriptionDefault
delta_gStandard ΔG°(kJ/mol)-10
tempTemperature (T)(K)298

How It Works

Equilibrium Constant from ΔG°

Formula

K = e^(−ΔG° / RT)

Equivalently: ΔG° = −RT ln(K)

Where:

  • K = equilibrium constant
  • ΔG° = standard Gibbs free energy change (J/mol)
  • R = 8.314 J/(mol·K)
  • T = temperature (K)

    • Large K (K >> 1) means products are favored. Small K (K << 1) means reactants are favored.

    Worked Example

    A reaction with ΔG° = -10 kJ/mol at 298 K.

    delta_g = -10temp = 298
    1. 01K = e^(-ΔG°/RT)
    2. 02K = e^(-(-10000)/(8.314 × 298))
    3. 03K = e^(10000/2477.6)
    4. 04K = e^(4.036)
    5. 05K = 56.6

    Frequently Asked Questions

    What does the equilibrium constant tell you?

    K indicates the ratio of product to reactant concentrations at equilibrium. K > 1 favors products; K < 1 favors reactants.

    Does K change with temperature?

    Yes. K depends on temperature through ΔG° = -RT ln(K). For exothermic reactions, K decreases with increasing temperature.

    What is the difference between K and Q?

    K is the equilibrium constant (at equilibrium). Q is the reaction quotient (at any point). If Q < K, reaction proceeds forward; if Q > K, it proceeds backward.

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