Activity Coefficient Calculator
Calculate activity coefficients using the Debye-Hückel limiting law for dilute solutions
Calculate Activity Coefficient
Red = cations (positive), Blue = anions (negative)
For dilute solutions (typically < 0.01 M)
Absolute value of ion charge (e.g., 1 for Na⁺, 2 for Ca²⁺)
Debye-Hückel constant (mol⁻¹/²·kg⁻¹/²)
Activity Coefficient Results
Formula used: log γ = -A × z² × √I
Calculation: log γ = -0.5115 × 1² × √0
Solution behavior: Strong ionic interactions (γ < 1)
Solution Analysis
Example Calculation
NaCl Solution Example
Problem: Calculate the activity coefficient of Na⁺ in 0.01 M NaCl solution at 25°C
Given: Ionic strength (I) = 0.01 M, Charge number (z) = 1, Temperature = 25°C
Constant: A = 0.5115 mol⁻¹/²·kg⁻¹/² at 25°C
Calculation Steps
1. Apply Debye-Hückel equation: log γ = -A × z² × √I
2. Substitute values: log γ = -0.5115 × 1² × √0.01
3. Calculate: log γ = -0.5115 × 1 × 0.1 = -0.05115
4. Take antilog: γ = 10⁻⁰·⁰⁵¹¹⁵
Result: γ = 0.8890
Activity Coefficient Ranges
γ = 1
Ideal solution
Activity = concentration
γ < 1
Strong ionic interactions
Activity < concentration
γ > 1
Non-ideal behavior
Activity > concentration
Temperature Effects
Higher Temperature
Larger A constant → Lower γ values
Lower Temperature
Smaller A constant → Higher γ values
Standard Conditions
25°C, A = 0.5115 mol⁻¹/²·kg⁻¹/²
Calculation Tips
Valid for dilute solutions (< 0.01 M)
Use absolute value of charge number
Temperature affects the constant A
Higher charges give lower γ values
Understanding Activity Coefficients
What is an Activity Coefficient?
The activity coefficient (γ) is a factor that relates the activity of an ion to its concentration in solution. It accounts for deviations from ideal solution behavior due to ionic interactions, particularly important in electrolyte solutions.
Debye-Hückel Limiting Law
log γ = -A × z² × √I
For dilute solutions
Activity vs Concentration
Activity (a) = γ × concentration (c). In ideal solutions, γ = 1 and activity equals concentration. In real solutions, ionic interactions cause deviations from this ideal behavior.
Factors Affecting Activity Coefficients
Ionic Strength (I)
Higher I → Lower γ
More ions → stronger interactions
Charge Number (z)
Higher |z| → Lower γ
More charged ions interact stronger
Temperature (T)
Higher T → Higher A → Lower γ
Temperature affects dielectric constant
Note: The Debye-Hückel limiting law is most accurate for very dilute solutions (I < 0.01 M). For higher concentrations, extended equations are needed.