The key difference between homogeneous and heterogeneous equilibrium is that in homogeneous equilibrium, the reactants and products are in the same phase of matter whereas, in heterogeneous equilibrium, the reactants and products are in different phases.
Equilibrium is a state in which the concentrations of reactants and products remain constant. There are two types of equilibria as homogeneous equilibrium and heterogeneous equilibrium. These two types differ from each other according to the phase of matter of the reactants and products in the equilibrium.
CONTENTS
1. Overview and Key Difference
2. What is Homogeneous Equilibrium
3. What is Heterogeneous Equilibrium
4. Side by Side Comparison – Homogeneous vs. Heterogeneous Equilibrium in Tabular Form
5. Summary
What is Homogeneous Equilibrium?
Homogeneous equilibrium is a state in which the reactants and products are in the same phase of matter. Usually, the reactants and products are in a single solution. We call this type of reaction mixture as a homogeneous mixture. The chemical species that are in this mixture can be molecules, ions, or a combination of molecules and ions. Furthermore, the expression for the equilibrium constant of this type of reaction include concentrations of all the reactants and products. For example, mixing sulfur dioxide gas and oxygen gas gives sulfur trioxide gas, all reactants and products are in the gas phase. Then the reaction and equilibrium constant (K) are as follows:
2SO2(g) + O2(g) ⇌ 2SO3(g)
K = [SO3(g)]2/[SO2(g)]2[O2(g)]
What is Heterogeneous Equilibrium?
Heterogeneous equilibrium is a state in which the reactants and products are in different phases. There the phases can be any combination of solid, liquid, and gas phases. However, unlike in homogeneous equilibria, when writing the equilibrium constant for heterogeneous equilibrium, we have to exclude the concentrations of solids and pure liquids. For example, mixing carbon in solid form with oxygen gas gives carbon monoxide gas. Then the reaction and equilibrium constant (K) are as follows:
O2(g) + 2C(s) ⇌ 2CO(g)
K=[CO(g)]2/[O2(g)]
What is the Difference Between Homogeneous and Heterogeneous Equilibrium?
Equilibrium is a state in which the concentrations of reactants and products remain constant. There are two types of equilibria as homogeneous equilibrium and heterogeneous equilibrium. The key difference between homogeneous and heterogeneous equilibrium is that in homogeneous equilibrium, the reactants and products are in the same phase of matter whereas, in heterogeneous equilibrium, the reactants and products are in different phases.
Furthermore, when determining the equilibrium constant for homogeneous equilibria, we have to include concentrations of all the reactants and products; however, when determining the heterogeneous equilibria, we have to exclude the concentrations of solids and pure liquids and need to use the concentrations of other reactants and products. As an example, 2SO2(g) + O2(g) ⇌ 2SO3(g) is a homogeneous equilibrium and O2(g) + 2C(s) ⇌ 2CO(g) is an example for a heterogeneous equilibrium.
Below infographic tabulates the difference between homogeneous and heterogeneous equilibrium.
Summary – Homogeneous vs. Heterogeneous Equilibrium
Equilibrium is a state in which the concentrations of reactants and products remain constant. There are two types of equilibria as homogeneous equilibrium and heterogeneous equilibrium. The key difference between homogeneous and heterogeneous equilibrium is that in homogeneous equilibrium, the reactants and products are in the same phase of matter whereas, in heterogeneous equilibrium, the reactants and products are in different phases. Moreover, the equilibrium constant for homogeneous equilibria includes concentrations of all the reactants and products, while the equilibrium constant for heterogeneous equilibria have to exclude the concentrations of solids and pure liquids.
Reference:
1.“What are homogeneous and heterogeneous equilibrium reactions”. Study.com, Study.com, Available here.
2.“15.4: Heterogeneous Equilibria.” Chemistry LibreTexts, Libretexts, 18 Sept. 2019, Available here.
3. “Homogeneous versus Heterogeneous Solution Equilibria.” Boundless Biology. Lumen, Available here.
Image Courtesy:
1. “Mixtures and Pure Substances 2×2” By John Trombley – Own work (CC BY 4.0) via Commons Wikimedia