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Chemical Equilibrium is a type of reversible reaction. It refers to the state of a system in which the concentration of the reactant and the concentration of the products do not change with time.
- In chemical equilibrium, the properties of the system also do not change further.
- There is no change in the concentrations of the reactants and the products because of equal rates of the forward and reverse reactions.
- The type of system is claimed to be in a state of dynamic equilibrium.
- In chemical equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction.
- The concentration does not change with time.
- The rate of reaction in both forward and backward reactions is equal to zero.
- Chemical equilibrium is also known as dynamic equilibrium.
- Fizz coming out of a cold drink bottle is an example of such a reaction.
- There is a required amount of carbon dioxide dissolved in the liquid.
Key Terms: Chemical Equilibrium, Dynamic Equilibrium, Forward Reaction, Backward Reaction, Reactant, Le-Chatelier’s Principle, Reversible Reaction, Equilibrium, Homogenous Equilibrium, Heterogeneous Equilibrium, Catalyst
What is Chemical Equilibrium?
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Chemical Equilibrium is defined as the state of a system in which the concentration of the reactant and the concentration of the products do not change with time.
- In the state of chemical equilibrium, the rate of the forward reaction is equivalent to the rate of the reverse reaction.
- The system does not display any further change in properties when it reaches the state of equilibrium.
- No change in the concentration of products and reactants.
- A graph with the concentration on the coordinate axis also called the x-axis.
- Time on the coordinate axis also called the y-axis is a forethought.
- Once the concentration of each reactant and product stops showing modification, chemical equilibrium is achieved.
Examples of What is Chemical EquilibriumExample: In chemical reactions, reactants are converted into products by the forward reaction, and also the product could also be converted into reactants by the backward reaction. The two states, reactants, and products are completely different in composition.
N2O4 ⇌ 2NO2 PCl5 ⇌ PCl3 +PCl2 N2 + 3H2 ⇌ 2NH3 |
Chemical Equilibrium
Types of Chemical Equilibrium
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There are two types of chemical equilibrium:
Homogeneous Chemical Equilibrium
In Homogeneous Chemical Equilibrium type, the reactants and the product of the chemical equilibrium are in the same phase. Homogenized equilibrium can be divided into two types:
(A) Reactions within which the quantity of molecules of the product is adequate to the number of molecules of the reactants. For instance,
- H2 (g) + I2 (g) ⇌ 2HI (g)
- N2 (g) + O2 (g) ⇌ 2NO (g)
(B) Reactions within which the amount (the quantity) of molecules of the product isn't adequate to the full number of chemical molecules. For instance,
- 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
- COCl2 (g) ⇌ CO (g) + Cl2 (g)
Heterogeneous Chemical Equilibrium
In Heterogeneous Chemical Equilibrium type, the reactants and also the product of chemical reaction are given in different phases.
Example of Heterogeneous Chemical EquilibriumExample: Many examples of heterogeneous equilibrium are listed below.
Thus, the various kinds of chemical reactions are supported by the parts of reactants and products. |
Factors affecting Chemical Equilibrium
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According to Le-Chatelier’s principle, if there's any modification within the factors affecting the equilibrium conditions, the system can counteract or scale back the result of the general transformation.
- This principle is applicable to each chemical and physical equilibrium.
- Factors like temperature, pressure, and concentration of the system that have an effect on the equilibrium.
- Some necessary factors affecting chemical reactions are mentioned below.
Change in Concentration
The concentration of the reactants or products included is eased by the reaction that consumes the substance that is added. It is removed by the equilibrium that is within the direction that replenishes the substance that is removed.
- When the concentration of the chemical or product is modified, the composition of the mixture in a chemical reaction gets modified.
Change in Pressure
Change in pressure happens due to the modification within the volume. If there's a modification in pressure it will have an effect on the aerosolized reaction because the total variety of aerosolized reactants and products are completely different.
- In process is continued with Chatelier's principle, in heterogeneous chemical reactions.
- The modification of pressure in all liquids and solids is unheeded as a result of the amount of pressure.
Change in Temperature
The result of temperature on chemical reaction depends upon the sign of ΔH of the reaction and follows Le-Chatelier’s Principle. As temperature increases the equilibrium constant of the associated reaction decreases.
- In association with the chemical reaction, the constant will increase with a rise in temperature.
- The speed of reaction is additionally full of the modification in temperature.
- Equilibrium shifts towards the chemical aspect, once the temperature will increase just in case of exothermic reactions.
- For endothermic reactions the equilibrium shifts towards the merchandise aspect with a rise in temperature.
Effect of a Catalyst
A catalyst does not have an effect on the chemical reaction. It solely hastens a reaction. In fact, the catalyst equally hastens the forward yet the reverse reaction. This ends up in the reaction reaching its equilibrium state quicker.
- The same quantity are given at an equilibrium state in an exceedingly catalyzed or a non-catalyzed reaction.
- The presence of a catalyst facilitates the reaction to proceed through a lower-energy transition state.
Effect of Addition of Associate Inert Gas
When an associate inert gas like argon (atomic number 18) is added to a continuing volume, it doesn't participate in the reaction and the equilibrium remains undisturbed.
- If the gas added may be a chemical or product concerned within the reaction, then the reaction quotient can modify.
Importance of Chemical Equilibrium
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Chemical Equilibrium is helpful in several industrial processes like,
Preparation of Ammonia by Haber’s Process
In this N (nitrogen) combines with a chemical element to create ammonia, the yield of ammonia is a lot more at high temperature, pressure and within the presence of iron as a catalyst.
Preparation of Acid by Contacts Method
In this process, the elemental reaction is the chemical reaction of pollutants into sulfur oxide. This involves chemical equilibrium.
| Class 11 Chemistry Related Concepts | ||
|---|---|---|
| Relationship between Kp and Kc | Homogeneous Equilibria | Gibbs Free Energy Formula and Example |
| Atomic Mass of Elements | Freezing Point Depression | Pressure of an Ideal Gas |
Problems on Chemical Equilibrium
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Given below are a few problems that can help one to understand the concept of chemical equilibrium better:
Solved ExamplesProblem 1: The constant KP for the reaction N2 (g) + 3H2 (g) ⇌ 2NH3 (g) is 1.6 × 10-4 atm-2 at 400°C. What's going to be the constant of the chemical reaction at 500°C if the warmth of the reaction at this temperature varies from -25.14 kcal? Solution: Equilibrium constants at completely different temperatures and the warmth of the reaction are connected by the equation, log KP2 = -25140/2.303 × a pair of [773 – 673 / 773 × 673] + log 1.64 × 10-4 log KP2 = -4.835 KP2 = 1.462 × 10-5 atm-2 Problem 2: Given N2 (g) + 3H2 (aq) ⇌ 2NH3 (g). Find Q and confirm the direction the reaction can shift so as to achieve the state of a chemical reaction. Solution: Given, [N2] = 0.04M, [H2] = 0.09M, and K = 0.040 Since solely N and H concentration is given, it is assumed as reactants and ammonia as a product. Since ammonia concentration is not given, it is assumed to be zero. As Q is the quantitative relation of the relative concentration of product to reactants, here Q =0. Since K = 0.04 is larger than Q, N and H will create the product ammonia. |
Things to Remember
- Chemical equilibrium is the balanced state of the system.
- In this the reactants and products do not change with time so that there is no further change in the properties of the system.
- The rate of the forward reaction in a system is equal to the rate of the reverse reaction.
- There are two types of chemical equilibrium namely Homogeneous and Heterogeneous chemical equilibrium.
- There are a lot of factors that affect the equilibrium of a system like the temperature, pressure, and concentration of the system.
- NCERT Solutions For Class 11 Chemistry Equilibrium and Equilibrium MCQ will help you prepare for examination.
Previous Years’ Questions (PYQs)
- At certain temperature, 50% of HI is dissociated into… (NEET 1994)
- The dissociation constants for acetic acid and HCN… (NEET 2009)
- Hydrolysis of sucrose is given by the following reaction… (NEET 2020)
- The value of equilibrium constant of the reaction,... (NEET 2008)
- At 25 degrees celsius, the dissociation constant of a base, BOH is… (NEET 2005)
- Three moles of PCl5, three moles of PCl3 and two moles of… (KCET 2008)
- A buffer solution has equal volumes of… (KCET 2005)
- Hydrogen ion concentration of an aqueous solution is… (KCET 2001)
- At a certain temperature in a 5 L vessel, 2 moles of carbon monoxide… (JEE Main 2018)
- In which of the following reactions, an increase in the volume… (JEE Main 2018)
Sample Questions
Ques. What is the result of a catalyst on a chemical equilibrium? (3 Marks)
Ans. A catalyst has no result in the chemical reaction. Because the catalyst carries out both forward and backward reactions in the same way, equally. Hence there is no net change in the relative number of forward as well as backward reactions.
- Thus, a catalyst has no effect on the equilibrium.
- A catalyst mainly accelerates the reaction.
- It makes the forward and backward reaction rate higher, so as to reach its equilibrium state as soon as possible.
Ques. What is the result of temperature on constant throughout associate exoergic reaction? (3 Marks)
Ans. With an increase in temperature, the constant decreases throughout the associated reaction. In an exothermic reaction, the system internally generates extra heat energy.
- When a chemical reaction, in which chemical energy is converted to thermal energy is generated.
- Hence, when the system generates heat energy from the inside, then this energy can be used to carry out a lot of work.
Ques. What is the result of the addition of argon throughout chemical equilibrium? (3 Marks)
Ans. There is no result on chemical equilibrium in addition to argon. Argon is an inert gas and when an inert gas is added to a volume that is constant, it does not affect the reaction so the equilibrium remains undisturbed. If the gas involved is a reactant or a product that gets involved in the reaction, then the reaction quotient changes.
Ques. What is meant by the forward reaction? (3 Marks)
Ans. A reaction within which the reactants are converted to products solely is termed a forward reaction. It is a reaction in which products are produced from reactants and it goes from left to right in a reversible reaction.
- Any forward reaction moves to the right side where the product or products are formed.
Ques. What is meant by the backward reaction? (3 Marks)
Ans. A reaction within which the products are converted back to reactants is termed a backward reaction. It tends to increase the resistance to transfer in a bigger amount. If the backward reaction rate is very large compared to the forward reaction rate, the transfer rate reaches its highest value. Then, as the forward reaction rate decreases, the transfer rate begins to decline.
Ques. What is Le Chatelier’s Principle? (2 Marks)
Ans. Le-Chatelier’s principle is described as: “A change in any of the components of an equilibrium that determines the equilibrium conditions of a system which will affect the equilibrium in such a way that the effect of the change is reduced or counteracted”. This applies to both physical and chemical state equilibrium.
Ques. What happens after equilibrium is reached? (2 Marks)
Ans. Chemical equilibrium is a constantly running process. The forward and reverse reactions continue to occur even after the equilibrium state has been reached. However, the ratio of the reactants and products becomes the same here, and hence there is no change in the relative concentrations of reactants and products for a reaction that is at equilibrium.
Ques. What is the Equilibrium equation? (2 Marks)
Ans. The equilibrium equation for a chemical reaction is expressed in terms of the concentration of the products and reactants. Chemical species only in aqueous and gaseous phases are included in the equilibrium equation because the concentrations of liquids and solids does not change.
Ques. Explain why pure solids and liquids can be ignored while writing the equilibrium constant expressions. (5 Marks)
Ans. The concentration of pure liquids and solids in the equilibrium expression for heterogeneous reactions is ignored because their concentrations remain constant.
- The concentration of pure solid and liquid remains almost the same( it changes by a very, very small fraction).
- And the molecular mass and density (at a particular temperature) of a pure substance are always fixed and are accounted for in the equilibrium constant. Therefore, the values of pure substances are not stated in the equilibrium constant expression.
Ques. The constant KP for the reaction N2 (g) + 3H2 (g) ⇌ 2NH3 (g) is 1.6 × 10-4 atm-2 at 400°C. What's going to be the constant of the chemical reaction at 500°C if the warmth of the reaction at this temperature varies from -35.14 kcal. (5 Marks)
Ans. Equilibrium constants at completely different temperatures and the warmth of the reaction are connected by the equation,
log KP2 = -35140/2.303 × a pair of [773 – 673 / 773 × 673] + log 1.64 × 10-4
log KP2 = -4.835
KP2 = 1.462 × 10-5 atm-2
Ques. Given N2 (g) + 3H2 (aq) ⇌ 2NH3 (g). Find Q and confirm the direction the reaction can shift so as to achieve the state of a chemical reaction. (5 Marks)
Ans. Given, [N2] = 0.06M, [H2] = 0.03M, and K = 0.060
Since solely N and H concentration is given, it is assumed as reactants and ammonia as a product. Since ammonia concentration is not given, it is assumed to be zero.
As Q is the quantitative relation of the relative concentration of product to reactants, here Q =0.
Since K = 0.06 is larger than Q, N and H will create the product ammonia.
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