Equilibrium Constant Calculator

Calculate the equilibrium constant (Kc) for chemical reactions and determine equilibrium position

For reaction: aA + bB ⇌ cC + dD
Kc = ([C]c × [D]d) / ([A]a × [B]b)

Enter the product of all product concentrations raised to their coefficients divided by the product of all reactant concentrations raised to their coefficients.

Product of product concentrations with stoichiometric coefficients as exponents

Product of reactant concentrations with stoichiometric coefficients as exponents

Understanding Equilibrium Constants

The equilibrium constant (Kc) is a fundamental concept in chemistry that quantifies the ratio of products to reactants at equilibrium for a reversible reaction. It tells us which direction a reaction favors and how far it proceeds before reaching equilibrium.

The Equilibrium Constant Expression

For the general reaction:

aA + bB ⇌ cC + dD

Kc = ([C]c × [D]d) / ([A]a × [B]b)

Products over reactants, raised to stoichiometric coefficients

Kc = Equilibrium constant

Dimensionless or with concentration units depending on reaction

[A], [B], [C], [D] = Molar concentrations

Equilibrium concentrations in mol/L (M)

a, b, c, d = Stoichiometric coefficients

Numbers in the balanced chemical equation

Interpreting K Values

K >> 1 (e.g., K = 10⁶)

• Equilibrium lies far to the right
• Products strongly favored
• Reaction goes nearly to completion
• Very little reactants remain

K ≈ 1 (e.g., 0.1 < K < 10)

• Equilibrium position is intermediate
• Significant amounts of both reactants and products
• Neither side is strongly favored

K << 1 (e.g., K = 10⁻⁶)

• Equilibrium lies far to the left
• Reactants strongly favored
• Very little reaction occurs
• Very little products form

Practical Example

Formation of Hydrogen Iodide

H₂(g) + I₂(g) ⇌ 2HI(g)

At equilibrium at 448°C:

  • [H₂] = 0.0222 M
  • [I₂] = 0.0222 M
  • [HI] = 0.156 M

Kc = [HI]² / ([H₂] × [I₂])
Kc = (0.156)² / (0.0222 × 0.0222)
Kc = 0.0243 / 0.000493
Kc = 49.3

Since K > 1, the forward reaction is favored, and significant HI is formed at equilibrium.

Key Concepts

⚖️ Dynamic Equilibrium

Forward and reverse reactions occur at equal rates

🌡️ Temperature Dependent

K changes with temperature but not with pressure or concentration changes

🔄 Reaction Quotient (Q)

Q has same form as K but uses non-equilibrium concentrations

⚗️ Le Chatelier's Principle

System shifts to counteract changes and restore equilibrium

Relationship Between K and Q

Predicting Reaction Direction

  • Q < K: Reaction proceeds forward (→) to form more products
  • Q = K: System is at equilibrium, no net change
  • Q > K: Reaction proceeds in reverse (←) to form more reactants

Applications

  • 🏭
    Industrial Chemistry: Optimize reaction conditions for maximum product yield (Haber process, contact process)
  • 🧪
    Analytical Chemistry: Predict solubility, precipitation, and complex formation
  • 💊
    Biochemistry: Understand metabolic pathways and enzyme-substrate equilibria
  • 🌊
    Environmental Science: Calculate CO₂ dissolution, acid-base equilibria in natural waters
  • 🔬
    Research: Design experiments, predict reaction feasibility, calculate equilibrium compositions

⚖️Quick Reference

Units:

Usually dimensionless or Mn

Formula:

Kc = [products] / [reactants]

Rule:

K > 1: products favored
K < 1: reactants favored

Level:

College Chemistry

🔗Related Calculators

📐Related Formulas

🎯Where It's Used

  • 🏭

    Industrial Processes

    Optimize chemical production

  • 🧪

    Analytical Chemistry

    Predict reaction outcomes

  • 💊

    Biochemistry

    Metabolic equilibria

  • 🌍

    Environmental Science

    Natural chemical processes