Heterogeneous Equilibrium

Introduction

Heterogeneous equilibrium is a chemical equilibrium in which all of the reactants and products are in distinct phases. A homogeneous equilibrium exists when all the reactants and products are in the same phase.

Chemical equilibrium is defined as the pace at which forward and backward reactions occur. According to the phase of the reactants and products, there are two forms of equilibrium. equilibrium between homogeneity and heterogeneity. When the reactants and products of an equilibrium process come together to form a single phase, whether it be a gas or a liquid, this is known as homogeneous equilibrium. In such situations, the reactants' and products' concentrations can vary greatly. On the other hand, a system with reactants, products, or both in more than one phase is said to be in a heterogeneous equilibrium, such as when a gas reacts with a solid or liquid.

What is Chemical Equilibrium?

In 1803, Berthollet discovered that some chemical reactions are reversible, which led to the conception of chemical equilibrium. Any reaction mixture must have equal forward and reverse reaction rates to be in equilibrium. For there to be chemical equilibrium, the rates of the forward reaction and the backward reaction must be equal.

If a chemical process is at the equilibrium state, the concentrations of reactants and products are stable or no longer tend to change over time. Chemical equilibria fall into one of two categories: homogeneous equilibria or heterogeneous equilibria, depending on the states of the reactants and products at equilibrium. The Greek words for "similar" and "different," respectively, are where the prefixes "homo" and "hetero" came from.

What is Heterogeneous Equilibrium ?

A heterogeneous equilibrium, as its name suggests, is one in which the reactants and products are both present in at least two distinct states of matter. For instance, the equilibrium response in the ice and water equilibrium system is depicted as follows −

$$\mathrm{H_2 O_{(S)} \leftrightarrow H_2 O_{(l)}}$$

As a result, in the equation above, the reactant and product states are different. There are two types of water in the system: liquid and solid. Because the states or phases of the reactant and product differentiation in an equilibrium system, it is known as a heterogeneous equilibrium system. A case of heterogeneous equilibrium is the breakdown of calcium carbonate into calcium oxide and carbon dioxide.

Since the reactants and products are present at various stages, heterogeneous equilibrium's equilibrium constant expression differs from that of homogeneous equilibrium. The concentrations of reactants and products are not measured when they are present in pure liquid or solid phases during equilibrium.

Examples of Heterogeneous Equilibrium

Below are a few typical instances of chemical reactions that take place at heterogeneous equilibrium.

• Bromine naturally exists as a liquid at room temperature. It easily turns into vapours and is crimson in color in both stages. Both the rate of bromine vapour condensation and evaporation are identical at equilibrium. The formula for the equation is

  $$\mathrm{Br_{2(l)} \leftrightarrow Br_{2(S)}}$$

  It is a heterogeneous equilibrium system because bromine exists as both a reactant and a product in multiple phases, and the system is in equilibrium.

• Another example of a heterogeneous equilibrium system is the reaction between carbon and carbon dioxide. When solid carbon and gaseous carbon dioxide mix, gaseous carbon monoxide is produced. In this equilibrium process, the rates of the forward and backward reactions are identical. The equation reads as follows −

  $$\mathrm{CO_{2(g)} + C_{(s)} \rightarrow 2CO_{(g)}}$$

  You can observe that the aforementioned equilibrium reaction is heterogeneous due to the presence of both reactants and products in solid or gaseous form.

• Another illustration of heterogeneous equilibrium is the reaction between chlorine gas and PCl₃at equilibrium. Because chlorine participates as gas and forms phosphorus pentachloride in a solid state in this equilibrium system, phosphorus trichloride happens in a liquid state. The formula is as follows −

  $$\mathrm{PCl_{3(g)} + Cl_{2(g)} \leftrightarrow PCl_{5(S)}}$$

• The interaction of steam with extremely heated carbon is another prominent illustration of heterogeneous equilibrium. Below is the equation −

  $$\mathrm{H_2 O_{(g)}+ C_{(s)} \leftrightarrow H_{2(g)} + CO_{(g)}}$$

  As you can see, the above-mentioned reaction is in equilibrium, with red hot carbon in the solid phase and water steam, carbon monoxide, and hydrogen in the gaseous phase. As a result, it serves as an illustration of heterogeneous equilibrium.

Equilibrium Constant of Heterogeneous Equilibrium Reaction

The link between products and reactants is expressed by the equilibrium constant for a process at equilibrium. K_C is used to indicate it. In K_C, C stands for concentration since concentrations of the reactants and products are used in the derivation of the equilibrium constant. Take a look at the typical response provided below, for instance −

$$\mathrm{aA + bB ↔ cC + dD}$$

$$\mathrm{K_{C} = \frac{[C]^c [D]^d}{[A]^{a}[B]^b}}$$

The concentrations of solids, pure liquids, and solvents are not included in heterogeneous equilibrium because they do not vary significantly with temperature and are therefore treated as unity or 1. This is important to remember when formulating the equilibrium constant for a heterogeneous equilibrium reaction. Some of the examples are given below −

• The reaction of bromine (Equilibrium)

  $$\mathrm{Br_{2(l)} \leftrightarrow Br_{2(S)}}$$

  $$\mathrm{K_C =[Br_2]}$$

• The reaction of carbon and carbon dioxide

  $$\mathrm{CO_{2(g)} + C_{(s)} → 2CO_{(g)}}$$

  $$\mathrm{K_C= \frac{[CO]^2}{[CO_2]}}$$

Homogeneous Equilibrium Reactions

A reaction is said to be in equilibrium if all its reactants and products are in the same phase or material condition, which is referred to as a "homogeneous equilibrium reaction" or "homogeneous equilibrium." Think about how hydrogen and carbon monoxide react. The equation reads as follows −

$$\mathrm{CO_{(g)}+ 2H_{2(g)} \leftrightarrow CH_3 OH_{(g)}}$$

Because carbon monoxide, hydrogen, and methanol are all present in the reaction's gaseous form and the reaction is at equilibrium, it is known as a homogeneous equilibrium.

Conclusion

Heterogeneous equilibrium is defined as the equilibrium between reactants and products from several stages. In contrast, reactants and products are in the same phase during homogeneous equilibrium. Calculating the equilibrium constant will allow you to determine the response rate regardless of the equilibrium. Examples of heterogeneous equilibrium include the breakdown of calcium carbonate into calcium oxide and carbon dioxide, whereas examples of homogeneous equilibrium include the reaction of carbon monoxide with hydrogen to produce methanol.

FAQs

1. What is the difference between heterogeneous and homogeneous equilibrium?

Equilibrium in which all the reactants and products are in the same phase is homogeneous and, if reactants and products are in different phases it is heterogeneous.

2. Is decomposition of calcium carbon a homogeneous equilibrium reaction?

Yes, because calcium carbonate is in a solid state whereas products are in solid and liquid states. Hence it is a heterogeneous system. The reaction is given below −

$$\mathrm{CaCO_{3(s)} \leftrightarrow CaO_{(s)} + CO_{2(g)}}$$

3. What are the factors affecting chemical equilibrium?

Equilibrium is influenced by the system's temperature, pressure, and concentration.

4. Who discovered chemical equilibrium?

By F. H. van't Hoff, the theory of chemical equilibrium was developed (1884-1886).

5. What is the theory of chemical equilibrium?

When the rates of the forward and backward reactions are identical, chemical equilibrium is reached. This is the theory of chemical equilibrium.