Homogeneous and Heterogeneous Equilibria

Homogeneous and Heterogeneous Equilibria are two fundamental types of chemical equilibrium that describe how reactions reach balance depending on the phases of reactants and products. In homogeneous equilibrium, all substances are in the same phase (such as gases or aqueous solutions), while in heterogeneous equilibrium, reactants and products exist in different phases. Understanding these equilibria is crucial in predicting reaction behavior in laboratory and industrial processes.

Chemical equilibrium is a fundamental concept in chemistry where the rate of forward and backward reactions becomes equal. It is mainly classified into two types: homogeneous equilibrium and heterogeneous equilibrium. Understanding these is crucial for chemical industries and academic learning.

Table of Contents

• Homogeneous Equilibrium
• Heterogeneous Equilibrium
• Key Differences
• Equilibrium Constant Expressions
• Quiz
• MCQs
• FAQs

1. Homogeneous Equilibrium

In a homogeneous equilibrium, all reactants and products exist in the same phase (gas or aqueous).

• Involves reactions where all species are gases or in solution.
• Equilibrium constant includes all species in the same phase.

Example: Haber process: N2(g) + 3H2(g) ⇌ 2NH3(g)

2. Heterogeneous Equilibrium

In a heterogeneous equilibrium, reactants and products are in different phases.

• Pure solids and liquids are excluded from the equilibrium constant expression.
• Only gases and aqueous species are included.

Example: CaCO3(s) ⇌ CaO(s) + CO2(g)

Key Differences

Aspect	Homogeneous	Heterogeneous
Phases	Same phase	Different phases
K Expression	All species	Only gases/aqueous
Example	N2 + 3H2 ⇌ 2NH3	CaCO3(s) ⇌ CaO(s) + CO2(g)

Equilibrium Constant Expressions

Homogeneous: Kc = [NH3]^2 / ([N2] [H2]^3)

Heterogeneous: Kc = [CO2]

Quiz

1. Define homogeneous equilibrium with an example.
2. Why are solids excluded in heterogeneous equilibrium?
3. Write Kc for CaCO3(s) ⇌ CaO(s) + CO2(g).

MCQs

1. In heterogeneous equilibrium, which is excluded from K?
   (a) Gases (b) Aqueous (c) Solids (✔) (d) All
2. Which is homogeneous?
   (a) CaCO3(s) ⇌ CaO(s)+CO2(g) (b) N2+3H2 ⇌ 2NH3 ✔ (c) H2O(l) ⇌ H2+O2

FAQs

Q1: What is homogeneous equilibrium?
A: When all reactants/products are in the same phase.

Q2: Why exclude solids/liquids from K?
A: Their concentration remains constant.

Related: Chemical Equilibrium – Wikipedia