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Equilibrium refers to a situation in which the system and its surroundings show no obvious changes. Reactions take place in order to do this. Reactants conduct reactions that reduce their energy, and they will continue until they reach a low-energy state, where they will remain unless disturbed. Equilibrium is the term for this situation. This can be divided into two categories: physical and chemical equilibrium.
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Key Takeaways: Energy change due to change in equilibrium, Equilibrium, Energy, Reactants, Catalyst, Pressure
Read More: Number of Moles Formula
Definition of Equilibrium
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The chemical equilibrium is defined as a point where the concentrations of the reactants and products do not fluctuate over time. When we talk about equilibrium, we're talking about a situation where the rate of forward reaction (reactant to product) equals the rate of backward response (products to reactions). We may alternatively remark that the rate at which reactants become products is the same as the rate at which products become reactants. Equilibrium is denoted by the symbol \(\rightleftharpoons\).
Reactants \(\rightleftharpoons\) Products
Many examples of chemical equilibrium can be seen all around us. A bottle of carbonated beverage is an example. The liquid of dissolved carbon dioxide is in the bottle. In the area between the liquid and the bottle lid, there is also CO2 gas. CO2 is constantly moving from the liquid to the gas phase, as well as from the gas phase to the liquid phase. However, there appears to be no difference when looking at the bottle. This is the point at which the system's chemical equilibrium has been achieved (where the rate of the forward reaction is equal to the rate of backward reaction).
Important Points on Equilibrium
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The state of equilibrium occurs when there is no net change in the concentrations of reactants and products, but this does not imply that the processes have come to a halt. The forward and backward responses continue at the same pace at equilibrium.
- Reactant represents the concentration of reactants.
- Products represents the concentration of products
The ratio of reactants to products is constant at equilibrium, and this constant is known as the Equilibrium Constant and is symbolized by the symbol Keq.
For Example: considering the below chemical reaction:
A \(\rightleftharpoons\) B
Where A is the Reactant
B is a product
Forward reaction: A → B, where A evolves into B and has a rate constant kf (the rate at which the reaction is taking place). This is how the forward rate equation will look:
Ratef = kf A
To generate the product B, the rate of reaction is dependent on the concentration of reactant A.
Backward reaction: B → A, where B transforms into A and has a rate constant kr (the rate at which the reaction is taking place). This is how the backward reaction will look:
Rater = kr B,
So, based on the equilibrium definition:
The rate of formation of the product = the rate of formation of the reactant
Kf A = kr B (the forward reaction rate is the same as the backward reaction rate)
= Constant
Equilibrium conditions can be attained in either way, from reactants to products or backwards from products to reactants.
Formation of chemical equilibrium through forward and backward reactions
Energy Changes Due to Equilibrium
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1. Change in Concentration:
When a reaction mixture is in equilibrium, for example, you can add more reactants. The reaction will then change in order to offset the change, according to Le Chatelier's principle. If reactants are added, the reaction will shift towards the products, forming more products, and if products are added, the reaction will shift towards the reactant, forming fewer products.
2. Change in Pressure:
This can be accomplished simply by altering the container's volume. For instance, if we reduce the volume of a container (containing gasses) mechanically, the pressure inside the container will rise. The reaction will drift in a way to decrease the pressure because the alteration we made was to increase the pressure inside the container. By moving to the reaction's edge, this might be accomplished with only a few gas molecules.
3. Addition of an Inert Gas:
It has no effect to add inert gasses (Argon, Neon Krypton) to the reaction mixture at a constant volume. The total pressure will change with the addition of inert gas to the system at constant volume, but the partial pressure of compounds will remain unchanged.
4. Change in Temperature:
The movement of heat causes a temperature change when it raises or lowers the temperature. This causes the chemical equilibrium to move towards the product or reactant, which may be detected by studying the reaction and determining whether it is endothermic or exothermic.
- The Equilibrium constant for exothermic reactions lowers as the temperature rises.
- When the temperature rises, the Equilibrium constant rises for endothermic reactions.
5. Effect of Catalyst on Equilibrium:
The energy of activation of both forward and backward reactions is reduced when a catalyst is added to a reaction. As a result, both forward and backward responses grow in the same amount, maintaining the equilibrium. Catalysts are chemicals that speed up the rate of a reaction without being consumed in the process.
Read More: Elementary Reactions
Things to Remember
- The term "equilibrium" refers to a situation in which the system and its surroundings show no noticeable changes.
- Chemical equilibrium occurs when both reactants and products are present in concentrations that have no further tendency to change with time, resulting in no apparent change in the system's properties.
- Energy change due to equilibrium happens because of change in concentration, change in pressure, addition of an Inert Gas, change in temperature, effect of Catalyst on Equilibrium.
- Two types of equilibrium are Homogeneous Equilibrium and Heterogeneous Equilibrium
- Variations in temperature, concentration, and, in some situations, volume and pressure can disrupt equilibrium; volume and pressure changes will disrupt equilibrium
Read More: Relation between Molarity and Molality
Sample Questions
Ques. What is Equilibrium? What are the different Kinds of Equilibriums? (4 marks)
Ans. Because the speeds of the forward and reverse reactions are identical, and the concentrations of the reactants and products remain constant, the system's characteristics remain unchanged. The forward reaction is said to proceed at the same rate as the reverse reaction.
The types of equilibrium are as follows:
Homogeneous Equilibrium- All substances (reactants and products) are in the same condition, most often in the gas phase, in homogeneous equilibrium. In a liquid solution, there is only one form of homogeneous equilibria: the reaction between solutes. Chemical species might be molecules, ions, or a combination of both. In the reaction below, for example, all of the components are in the aqueous phase.
C2H2(aq) + 2Br2(aq) ↔ C2H2Br4(aq)
Heterogeneous Equilibrium- Substances (reactants and products) are found in two or more phases in heterogeneous equilibrium. Any combination of liquid and gas phases, as well as solid, liquid, and gas phases, is possible.
Ques. What role does energy play in maintaining equilibrium? What happens when an equilibrium system is perturbed? (2 marks)
Ans: The free energy differential between the two sides of the reaction will define the balance between reactants and products in a reaction. The larger the free energy differential, the more one side of the reaction will benefit.
Chemists say you put stress on the equilibrium when you change something in a reaction that is at equilibrium. When this happens, the reaction will no longer be in equilibrium, and it will begin adjusting the concentrations of reactants and products until it finds a new equilibrium point.
Ques. What are three factors that can induce an equilibrium shift? (2 marks)
Ans: The three factors are:
- Variations in temperature
- Concentration
- In some situations, volume and pressure can disrupt equilibrium.
Volume and pressure changes will disrupt equilibrium if the number of moles of gas on the reactant and product sides of the reaction differ.
Ques. What role does energy play in maintaining equilibrium? (2 marks)
Ans: The free energy differential between the two sides of the reaction will define the balance between reactants and products in a reaction. The larger the free energy differential, the more one side of the reaction will benefit.
Ques. What is equilibrium energy? Is it possible for the equilibrium constant to be infinite? (2 marks)
Ans: The equilibrium energy of a canonical system at a given temperature is equal to the energy required to achieve the same temperature in a microcanonical system. In this view, the two systems are equivalent, and the outcome demonstrates thermodynamic consistency.
Its value is independent of the reactant or product concentrations at the start. The values of the equilibrium constant, on the other hand, change with temperature, hence the equilibrium constant is never zero or infinite.
Ques. How do the equilibrium constant and free energy relate to one another? (2 marks)
Ans: When equilibrium is reached, there is no further change in free energy, i.e. ΔG = 0 and Q equals the equilibrium constant. As a result, the equation above becomes. Galvanic cells are an example of this. The electrical work done by the cell is related to Gibbs energy change ΔG.
Ques. What effect does temperature have on the equilibrium reaction? (2 marks)
Ans: The point of equilibrium shifts in the direction of the endothermic reaction as the temperature rises. When the temperature is lowered, the equilibrium position shifts in favor of the exothermic reaction.
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