Homogeneous Equilibrium

Homogeneous Equilibrium is a state in a chemical reaction where all reactants and products are in the same phase. In this equilibrium, the rate of forward and backward reaction remains the same.

In this article, we will cover the basic ideas of homogeneous equilibrium, equilibrium constant, examples of homogeneous equilibrium along with a few problems based on the concept.

What is Homogeneous Equilibrium?

Homogeneous equilibrium is a state in chemical reaction that occurs when all the reactants and products are in the same phase of matter (i.e., all gases, all liquids, or all solids). In simple terms, in homogenous equilibrium, there is no change in the physical state of the substances during the reaction.

In homogeneous equilibrium, the rate of the forward and reverse reactions are equal, therefore, the ratio of concentrations of reactants and products remains constant with time. This simply means that the reactants are continuously converting into products and vice versa at the same rate and time.

Equilibrium Constant in Gaseous Systems

In gaseous systems, the equilibrium constant, K_p​, represents the ratio of the partial pressures of products to the partial pressures of the reactants.

For a general reaction:

aA + bB ⇌ cC + dD

The equilibrium constant expression in terms of partial pressures (K_p​) is given by:

[Tex]K= \frac{[C]^c. [D]^d} {[A]^a. [B]^b}​[/Tex]

Where:

• [A], [B], [C], and [D] are the molar concentrations of the reactants and products at equilibrium,
• a, b, c, and d are the coefficients of the reactants and products in the balanced chemical equation.

The value of K_p​ depends only on the temperature and is constant at a given temperature. The value of Kp can be used to determine the nature of the reactants and products in the equilibrium reaction.

• If K​_p is much greater than 1, the products are favored at equilibrium.
• If K_p​ is much less than 1, the reactants are favored.
• If K_p​ is close to 1, equal amounts of both reactants and products are present at equilibrium.

Check, Applications of Equilibrium Constants

Equilibrium Constant K_p for a Few Selected Reactions

Equilibrium Constant K_p for a Few Selected Reactions is given in the table below:

Reaction	Temperature	Kp
N2​(g) + 3H2​(g) ⇌ 2NH3​(g)	298	6.8 × 105
	400	4.1
	500	3.6 × 10-2
N2​O4​(g) ⇌ 2NO2​(g)	298	0.98
	400	47.9
	500	1700
2SO2(g) + O2(g) ⇌ 2SO3(g)	298	4 × 1024
	400	2.5 × 1010
	500	3 × 104

Example of Homogeneous Equilibrium

Examples of homogenous equilibrium are:

Formation of Ammonia

When nitrogen and hydrogen gas react with each other ammonia is formed. The chemical equation of this reaction is:

N₂​(g) + 3H₂​(g) ⇌ 2NH_3​(g)

In this reaction, nitrogen, hydrogen, and ammonia are in the gaseous phase. As the reaction progresses, some nitrogen and hydrogen molecules combine to form ammonia, and some ammonia molecules decompose back into nitrogen and hydrogen.

Eventually, the forward and reverse reactions reach a balance where the concentrations of nitrogen, hydrogen, and ammonia remain constant.

Formation of Hydrogen Iodide

Formation of hydrogen iodide (HI) from hydrogen gas (H₂) and iodine gas (I₂) in the gas phase is another example of homogeneous equilibrium. The chemical equation of this reaction is:

H₂​(g) + I₂​(g) ⇌ 2HI(g)

During this reaction, hydrogen and iodine molecules combine to form hydrogen iodide, and some hydrogen iodide molecules decompose back into hydrogen and iodine.

Eventually, the forward and reverse reactions reach an equilibrium where the concentrations of hydrogen, iodine, and hydrogen iodide remain constant.

Read More,

• Difference Between Heterogeneous and Homogenous Equilibrium
• Heterogeneous Equilibria
• Law of Chemical Equilibrium and Equilibrium Constant
• Chemical Equilibrium

NCERT Problems on Homogeneous Equilibrium

Problem 1: PCl₅, PCl₃ and Cl₂ are at equilibrium at 500 K and having concentration 1.59M PCl₃, 1.59M Cl₂ and 1.41 M PCl₅. Calculate K_c for the reaction,

PCl₅ ⇄ PCl₃ + Cl_2.

Solution:

The equilibrium constant K_c for the above given reaction can be written as,

K_c = [PCl₃] [CL₂]/[PCl₅]

Given: [PCl₃] = 1.59M

[CL₂] = 1.59M and [PCl₅] = 1.41M

Putting value in the above formula we get:

K_c = 1.59 × 1.59/1.41

K_c = 1.79

Problem 2: For the equilibrium, 2NOCl(g) ⇄ 2NO(g) + Cl₂(g) the value of the equilibrium constant, K_c is 3.75 × 10^–6 at 1069 K. Calculate the K_p for the reaction at this temperature?

Solution:

We know, K_p = K_c(RT)^∆n

Given, K_c = 3.75 ×10^–6

T = 1069 K and R = 0.0831

Also, from the above reaction,

∆n = (2+1) – 2 = 1

Putting values in the formula we get:

K_p = 3.75 ×10^–6 (0.0831 × 1069)¹

K_p = 0.033

FAQs on Homogeneous Equilibrium

What is homogeneous equilibrium?

Homogeneous equilibrium occurs in a chemical reaction where all reactants and products are in the same phase and the concentrations of reactants and products remain constant with time.

What is an example of homogeneous equilibrium reaction?

An example of a homogeneous equilibrium reaction is:

2NO₂​(g) ⇌ 2NO(g) + O_2​(g)

In this reaction, both the reactants and the products are in the gas phase, making it a homogeneous equilibrium.

What is relationship between K_P and K_C?

The relationship between K_P and K_C is determined by the ideal gas law using the equation: K_P = K_C × (RT)^Δn, where Δn is the difference in the number of moles of gaseous products and reactants.

What is difference between homogeneous and heterogeneous equilibrium?

In homogeneous equilibrium, all reactants and products are in the same phase whereas in heterogeneous equilibrium, reactants and products are in different phases.