How to Calculate Keq From Ka

Equilibrium Constant from Acid Dissociation Constant:

\[ K_{eq} = K_a \text{ for weak acids} \quad (K_{eq} = \frac{[H^+][A^-]}{[HA]}) \]

Equilibrium Constant (Keq):

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1. What is the Relationship Between Keq and Ka?

The equilibrium constant (Keq) for weak acids is equal to the acid dissociation constant (Ka). This relationship holds because the dissociation of weak acids represents the equilibrium between the acid and its ions in solution.

2. How Does the Calculator Work?

The calculator uses the fundamental relationship:

\[ K_{eq} = K_a \quad \text{for weak acids} \]

Where:

\( K_{eq} \) — Equilibrium constant (dimensionless)
\( K_a \) — Acid dissociation constant (mol/L)
\( K_a = \frac{[H^+][A^-]}{[HA]} \) — Definition of acid dissociation constant

Explanation: For weak acids, the equilibrium constant for the dissociation reaction is identical to the acid dissociation constant, as both represent the same chemical equilibrium process.

3. Importance of Equilibrium Constant Calculation

Details: Understanding the relationship between Keq and Ka is crucial for predicting acid behavior in solution, calculating pH, and understanding chemical equilibrium in acid-base chemistry.

4. Using the Calculator

Tips: Enter the acid dissociation constant (Ka) in mol/L. The value must be positive and greater than zero. The calculator will return the equilibrium constant (Keq) as a dimensionless quantity.

5. Frequently Asked Questions (FAQ)

Q1: Why is Keq equal to Ka for weak acids?
A: Because the acid dissociation process itself represents the equilibrium reaction, so the equilibrium constant equals the acid dissociation constant.

Q2: Does this relationship hold for strong acids?
A: No, strong acids completely dissociate in water, so their Ka values are very large and the concept of equilibrium constant doesn't apply in the same way.

Q3: What are typical Ka values for weak acids?
A: Weak acids typically have Ka values between 10^-2 and 10^-10 mol/L, with smaller values indicating weaker acids.

Q4: How does temperature affect Ka and Keq?
A: Both Ka and Keq are temperature-dependent. The relationship Keq = Ka remains valid at any given temperature.

Q5: Can this calculator be used for bases?
A: No, this specific relationship applies only to weak acids. For weak bases, you would use Kb (base dissociation constant).