Chemical Equilibrium and Factors Affecting it

A simple chemical reaction is a change in the concentration of reactants and the formation of products. When the system reaches the stage in which there is no further change in concentration of reactants or products with time, the state is known as a chemical equilibrium. In this state, neither the concentration of the reactants is changed with time, nor is the formation of products. The reaction reaches a static state without further bond breakage or bond formation. In other words, chemical equilibrium is a state in which the rate of forwarding reaction is equal to the rate of the backward or reverse reaction. In concentration chemistry, the equilibrium state doesn’t prefer the change in concentration of the substances involved. Let’s understand everything about chemical equilibrium in detail! 

What is the equilibrium stage? 

Also known as dynamic equilibrium, this stage is the state when the rate of forwarding and backward reaction becomes equivalent. In other words, the number of reactants that have been converted into products and the number of products that have been converted into reactants is the same. There are numerous other factors like concentration, temperature, pressure and catalyst that affect the equilibrium state in a particular reaction. 

Types of chemical equilibrium 

Generally, there are two main types of chemical equilibrium. Although both chemical equilibria involve the reactants and products, they are a little different from each other. Here are both the types of chemical equilibrium explained. 

1. Homogeneous Chemical Equilibrium – 

The reactions in which both the reactants and products involved are in the same phase or state. That is, either the reactants and products will be present in a gaseous state, or they all would be in a solid or liquid state. Meaning no state or phase difference is allowed in inhomogeneous chemical equilibrium. These reactions are further divided into two categories:

The reactions in which the number of molecules in reactants is equal to the number of molecules of products. Let’s understand the type by taking an example.

1)  H2 (g) + I2 (g) ⇌ 2HI (g)

2)  N2 (g) + O2 (g) ⇌ 2NO (g)

Another type of homogeneous reaction is the reaction in which the number of reactants is not equal to the number of molecules of the products. Let’s take an example to know more about the type. 

 1) 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

2) COCl2 (g) ⇌ CO (g) + Cl2 (g)

2.  Heterogeneous Chemical Equilibrium 

Another type of chemical equilibrium is in which the reactants react and the products formed are in different states. Some of the reactants involved can be solid, whereas others can be gas, solid or liquid. Here are a few examples of heterogeneous chemical equilibrium. 

 1) CO2 (g) + C (s) ⇌ 2CO (g) 

2) CaCO3 (s) ⇌ CaO (s) + CO2 (g)

Hence, chemical equilibrium is wholly based on the phase of reactants and products. 

Factors affecting Chemical Equilibrium 

As per Le-Chatelier’s principle, certain factors directly affect chemical equilibrium. These are concentration, temperature, pressure and catalyst; if any of the factors alter, it directly impacts the state of chemical equilibrium. Both physical and chemical equilibrium work is based on Le-Chatelier’s principle. Here are the other factors related to the chemical equilibrium. 

Change in Concentration 

When the concentration of the solution changes, it directly influences the chemical equilibrium state of the reaction. Here are three main points of how a concentrated solution influences chemical equilibrium. 

1) When the concentration of the reactants increases, the reaction moves towards the direction in which the added reactant gets consumed. If the amount on the reactant side is increased, the reaction will tend to move forward. 

2) Alternatively, when the concentration of the reactants is decreased. The reaction tends to move in a backward reaction to attain chemical equilibrium. Meaning if the amount on the product side gets increased, the reaction will tend to move in the backward direction. 

3)  During the change in concentration of reactants and the products, the composition of the mixture also gets influenced.

Pressure Change 

In any reaction, the change in pressure is directly linked to the change in volume. When the pressure in any reactant or product changes, it directly changes the gaseous reaction. 

Change in Temperature 

Among the different factors concentration, temperature, pressure and catalyst related to equilibrium reaction, temperature plays a vital role in the reaction. Temperature and equilibrium constant are inversely proportional to each other. If the temperature increases in a particular reaction, the equilibrium constant decreases. The condition is that the reaction should be exothermic. Alternatively, the equilibrium constant increases with the increase in temperature in the endothermic reaction. Aside from the change in equilibrium constant, the rate of chemical reaction gets influenced by the change in temperature. This concept is based on Le-Chatelier’s principle, in which the chemical equilibrium shifts on the reactant side when the temperature is increased. But the reaction should be exothermic. 

Effect of Catalyst

When directly influencing the chemical equilibrium, the catalyst does not play a significant role. But its function is to speed up the reaction. The use of a catalyst equally increases the speed of the forward and backward reactions. This, in turn, helps the reaction reach the equilibrium state at a much faster pace. Catalyst provides the reaction with an alternative path of lower energy. Meaning the reaction can easily reach the equilibrium state using a catalyst. 

Examples of Chemical Equilibrium 

In any chemical reaction, the reaction starts with different reactants and products. The reactants are directly changed to products, and at the start, the two compositions are different. But as the reaction proceeds, a point reaches when the rate of forwarding and backward reaction becomes equivalent. Here are a few examples representing chemical equilibrium. 

1)   N2O4 ⇌ 2NO2

2)   PCl5 ⇌ PCl3 +PCl2

3)   N2 + H2 ⇌ 2NH3

 Conclusion

When any chemical reaction occurs, it directly influences the concentration of reactants present in it. On the other side, new products are formed with the new bond formation. When a reaction isn’t possible, this state is known as the chemical equilibrium state, and the product formation stops. The time in which the chemical equilibrium is reached in a particular reaction directly depends on multiple factors like concentration, temperature, pressure and catalyst. We hope this article will help you get a deep insight into chemical equilibrium and the factors that influence it.