Activity Coefficient Calculator

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Single-ion: one species in solution. Mean ionic: combines cation and anion contributions for a dissolved salt such as NaCl or CaCl2.
Limiting law: very dilute solutions (I < 0.01 mol/kg). Extended DH: up to ~0.1 mol/kg. Davies: up to ~0.5 mol/kg.
I = 0.5 x sum(c_i x z_i^2). If you know only the salt concentration, multiply by the ion factor: 1 for 1:1 salts (NaCl), 3 for 2:1 or 1:2 salts (CaCl2, Na2SO4), 4 for 2:2 salts (MgSO4).
mol/kg
Absolute value of the ion charge. For Na+ or Cl- enter 1; for Ca2+ or SO42- enter 2; for Al3+ enter 3.
Hydrated ionic radius used in the extended Debye-Huckel denominator. Typical values: 0.25-0.4 nm for monovalent ions, 0.5-0.9 nm for divalent/trivalent. Not used by the limiting law or Davies equation.
nm
Solution temperature affects the dielectric constant of water and therefore the Debye-Huckel constants A and B. Range: 0-100 C at atmospheric pressure.
C
Activity coefficientModerate non-ideality
0.7601

Dimensionless correction factor (1 = ideal, <1 typical for electrolytes)

log10(gamma)-0.1191
A constant (at T)0.5331mol^(-1/2) kg^(1/2)
B constant (at T)3.2822nm^-1 mol^(-1/2) kg^(1/2)
Model reliabilityReliable (I <= 0.1 mol/kg)
Limiting law gamma0.6783
Extended DH gamma0.7601
Davies gamma0.7725
0.7601
Strong non-ideality<0.5Moderate non-ideality0.5-0.8Mild non-ideality0.8-0.99Near-ideal0.99+

Activity coefficient (extended Debye-Huckel equation): 0.7601

  • A coefficient of 0.7601 means the effective concentration (activity) of the ion is 76.0% of its analytical concentration, so the solution behaves less active than a simple dilution would predict.
  • The ionic strength entered is 0.1000 mol/kg. Reliable (I <= 0.1 mol/kg)
  • For comparison: limiting law gives 0.6783, extended Debye-Huckel gives 0.7601, and Davies gives 0.7725.

Next stepTo go further, multiply the calculated activity coefficient by the molar (or molal) concentration to get the thermodynamic activity, then substitute that into your equilibrium constant expression.

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