Learn about chemical equilibrium, factors affecting equilibrium, and ionic equilibrium in solutions. Understand the law of chemical equilibrium and equilibrium constant.
Chapter 6 of the Class 11 Chemistry textbook focuses on the concept of chemical equilibrium, a fundamental topic in physical chemistry. Equilibrium is a dynamic state where the concentrations of reactants and products in a reversible chemical reaction remain constant over time, even though the forward and reverse reactions continue to occur. This chapter is crucial for understanding various chemical processes, including industrial manufacturing, biological systems, and environmental chemistry. Students will learn about the dynamic nature of equilibrium, factors affecting equilibrium, and how to predict the direction of chemical reactions. The chapter also covers ionic equilibrium, acid-base theories, and the role of equilibrium in solutions. By mastering these concepts, students will be better equipped to understand and solve problems related to chemical and physical equilibria.
What you'll learn
1Understand the dynamic nature of chemical and physical equilibria
2Explain the law of chemical equilibrium and equilibrium constant
3Classify equilibria as homogeneous and heterogeneous
4Analyze factors affecting chemical equilibrium
5Describe ionic equilibrium in solutions
6Explain hydrolysis of salts and pH
7Calculate solubility product constants
Chapter at a glance
01Equilibrium and Dynamic Nature of Reactions
02Law of Chemical Equilibrium and Equilibrium Constant
03Homogeneous and Heterogeneous Equilibrium
04Factors Affecting Chemical Equilibrium
05Ionic Equilibrium in Solutions
06Hydrolysis of Salts and pH
Detailed chapter notes
01
Equilibrium and Dynamic Nature of Reactions
Equilibrium is a dynamic state where the concentrations of reactants and products in a reversible chemical reaction remain constant over time. This does not mean that the reactions have stopped; rather, the rates of the forward and reverse reactions are equal. The chapter introduces the concept of equilibrium with examples from both physical and chemical processes. Students will learn about the dynamic nature of equilibrium, where molecules continuously interconvert between different states, but the overall concentrations remain unchanged. This understanding is crucial for predicting the behavior of chemical systems and designing industrial processes.
Equilibrium is a dynamic state
Rates of forward and reverse reactions are equal at equilibrium
Examples include physical processes like phase changes and chemical reactions
02
Law of Chemical Equilibrium and Equilibrium Constant
The law of chemical equilibrium states that at a given temperature, the product of the concentrations of the products raised to their respective stoichiometric coefficients is constant and is equal to the product of the concentrations of the reactants raised to their respective stoichiometric coefficients. This constant is known as the equilibrium constant (K). The chapter explains how to write the equilibrium constant expression for any given chemical reaction and how to use it to predict the direction of the reaction. Students will also learn about the relationship between the equilibrium constant and the Gibbs free energy change, which is a measure of the spontaneity of the reaction.
Law of chemical equilibriumK = [products]/[reactants]
Equilibrium constant (K) is temperature-dependent
K is related to the Gibbs free energy change (ΔG)
03
Homogeneous and Heterogeneous Equilibrium
Equilibria can be classified as homogeneous or heterogeneous. In homogeneous equilibrium, all the reactants and products are in the same phase (e.g., all gases or all in solution). In heterogeneous equilibrium, the reactants and products are in different phases (e.g., solid and gas, or liquid and gas). The chapter discusses the differences between these two types of equilibria and how to write the equilibrium constant expressions for each. Students will learn to identify the phases involved in a reaction and to determine whether the equilibrium is homogeneous or heterogeneous.
Homogeneous equilibriumall reactants and products in the same phase
Heterogeneous equilibriumreactants and products in different phases
Equilibrium constant expressions differ for homogeneous and heterogeneous equilibria
04
Factors Affecting Chemical Equilibrium
The chapter explores the factors that affect chemical equilibrium, including concentration, pressure, temperature, and the presence of a catalyst. Le Chatelier's principle is introduced, which states that if a system at equilibrium is subjected to a change in concentration, pressure, or temperature, the system will adjust to counteract the change and restore equilibrium. Students will learn how to predict the direction of the reaction in response to these changes and how to control the yield of products in industrial processes by manipulating these factors.
Le Chatelier's principlesystems adjust to counteract changes
Factors affecting equilibriumconcentration, pressure, temperature, and catalysts
Predicting the direction of the reaction in response to changes
05
Ionic Equilibrium in Solutions
Ionic equilibrium refers to the dynamic state where ions in a solution are continuously interconverting between different forms. The chapter discusses the ionization of acids and bases in aqueous solutions and introduces the concept of the ionization constant (K). Students will learn about the different theories of acids and bases, including the Arrhenius, Brönsted-Lowry, and Lewis theories. The chapter also covers the role of water in ionic equilibria and the concept of the ionic product of water (Kw).
Ionic equilibriumdynamic state of ions in solution
Ionization of acids and bases in aqueous solutions
Theories of acids and basesArrhenius, Brönsted-Lowry, and Lewis
Ionic product of water (Kw)
06
Hydrolysis of Salts and pH
The chapter explains the hydrolysis of salts and its effect on the pH of the solution. Hydrolysis is the reaction of a salt with water to produce an acidic or basic solution, depending on the nature of the salt. Students will learn to predict the pH of a salt solution based on the hydrolysis reaction and to calculate the degree of hydrolysis. The chapter also discusses buffer solutions, which are solutions that resist changes in pH when small amounts of acid or base are added. Students will learn about the composition and function of buffer solutions and how to prepare them.
Hydrolysis of saltsreaction with water to produce acidic or basic solutions
Predicting the pH of a salt solution
Buffer solutionsresist changes in pH
Composition and function of buffer solutions
07
Solubility Product Constant
The solubility product constant (Ksp) is a measure of the solubility of a sparingly soluble ionic compound. The chapter explains how to write the solubility product expression for a given compound and how to use it to calculate the solubility of the compound in a given solution. Students will learn about the common ion effect, which is the decrease in solubility of a sparingly soluble compound in the presence of a common ion. The chapter also discusses the role of pH in the solubility of ionic compounds and how to predict the solubility of a compound in acidic or basic solutions.
Solubility product constant (Ksp)measure of solubility of sparingly soluble compounds
Writing the solubility product expression
Calculating the solubility of a compound
Common ion effectdecrease in solubility in the presence of a common ion
Role of pH in solubility of ionic compounds
Want the complete chapter resources?Topic notes, quizzes and flashcards for Equilibrium.
Which of the following best describes a dynamic equilibrium?
AThe reaction stops completely and no further changes occur
BForward and reverse reactions occur simultaneously at equal rates
COnly the forward reaction takes place at a measurable rate
DThe concentration of reactants becomes zero
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Answer: (B) Forward and reverse reactions occur simultaneously at equal rates
Dynamic equilibrium is characterized by forward and reverse reactions proceeding at the same rate, making macroscopic concentrations appear constant while molecular-level changes continue.
Question 02
The law of chemical equilibrium states that at a given temperature, the product of concentrations of reactants and products, each raised to the power of their stoichiometric coefficients, is constant. This constant is known as:
AEquilibrium constant (Kc or Kp)
BRate constant
CSolubility product
DIonization constant
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Answer: (A) Equilibrium constant (Kc or Kp)
The equilibrium constant (Kc or Kp) is defined by the law of chemical equilibrium and represents the ratio of products to reactants at equilibrium, each raised to their stoichiometric coefficients.
Question 03
Which of the following is an example of a homogeneous equilibrium?
AN₂(g) + 3H₂(g) ⇌ 2NH₃(g)
BCaCO₃(s) ⇌ CaO(s) + CO₂(g)
CFe(s) + H₂O(g) ⇌ Fe₃O₄(s) + H₂(g)
DAgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq)
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Answer: (A) N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
A homogeneous equilibrium involves all reactants and products in the same physical state. In N₂(g) + 3H₂(g) ⇌ 2NH₃(g), all species are gases, making it homogeneous.
Question 04
Which of the following statements correctly describes Le Chatelier's Principle?
AA system at equilibrium will shift to counteract any change imposed on it
BAn equilibrium system always moves toward products
CIncreasing temperature always shifts equilibrium to the right
DPressure changes do not affect equilibrium position
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Answer: (A) A system at equilibrium will shift to counteract any change imposed on it
Le Chatelier's Principle states that when a stress is applied to a system at equilibrium, the system shifts in a direction to relieve that stress. This is a fundamental principle governing equilibrium behavior.
Question 05
What is the ionic product of water (Kw) at 25°C?
A1.0 × 10⁻¹⁴
B1.0 × 10⁻¹²
C1.0 × 10⁻¹⁶
D1.0 × 10⁻¹⁸
Show answer
Answer: (A) 1.0 × 10⁻¹⁴
The ionic product of water (Kw = [H⁺][OH⁻]) is a constant value of 1.0 × 10⁻¹⁴ at 25°C, which is a fundamental constant in aqueous chemistry.
Ready for more practice?Unlock the full quiz for this chapter.
Q1. Define dynamic equilibrium. Why is the term 'dynamic' important when describing chemical equilibrium? Explain with reference to what happens at the molecular level.
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Model answer
Dynamic equilibrium is the state in which the rate of the forward reaction equals the rate of the backward reaction, and there is no net change in the concentration of reactants and products. The term 'dynamic' is important because it emphasizes that equilibrium is not static—reactions continue to occur in both directions simultaneously at the molecular level. Although macroscopically the concentrations appear constant, at the molecular level reactant molecules are continuously forming products while product molecules are continuously reforming reactants at equal rates.
Sample question3 marks
Q2. Define the Law of Chemical Equilibrium. State the mathematical expression for the equilibrium constant (Kc) for a general reaction: aA + bB ⇌ cC + dD, and explain what the equilibrium constant tells us about a reaction.
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Model answer
The Law of Chemical Equilibrium states that at a given temperature, the ratio of the product of concentrations of products raised to their stoichiometric coefficients to the product of concentrations of reactants raised to their stoichiometric coefficients is constant. Mathematically, Kc = [C]^c [D]^d / [A]^a [B]^b. The equilibrium constant tells us the extent of reaction: a large Kc value indicates the reaction proceeds largely to completion (products favored), while a small Kc value indicates the reaction barely proceeds (reactants favored).
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Q3. Define homogeneous equilibrium and heterogeneous equilibrium. Give one example of each type.
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Model answer
Homogeneous equilibrium is a state of equilibrium in which all reactants and products exist in the same physical phase (solid, liquid, or gas). For example, N₂O₄ ⇌ 2NO₂ (both gases). Heterogeneous equilibrium is a state of equilibrium in which reactants and products exist in different physical phases. For example, CaCO₃(s) ⇌ CaO(s) + CO₂(g), where solids and gas are present together.
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Q4. Explain how an increase in temperature affects a reversible exothermic reaction at equilibrium. What happens to the equilibrium position and the equilibrium constant?
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Model answer
When temperature increases for an exothermic reaction at equilibrium, the system shifts in the backward (reverse) direction to absorb the added heat, according to Le Chatelier's principle. This shifts the equilibrium position towards the reactants (left), reducing the yield of products. The equilibrium constant Kc decreases because it is temperature-dependent and favours the endothermic direction at higher temperatures.
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Q5. Define ionic equilibrium and explain why it is called a dynamic equilibrium. Give one example of an ionic equilibrium in an aqueous solution.
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Model answer
Ionic equilibrium is the state in which the concentration of ions in a solution remains constant because the rate of ionization of the electrolyte equals the rate of recombination of ions. It is dynamic because the forward process (ionization) and backward process (recombination) continue to occur simultaneously at equal rates, even though the observable concentrations remain unchanged. Example: When acetic acid (CH₃COOH) dissolves in water, it establishes an equilibrium: CH₃COOH ⇌ CH₃COO⁻ + H⁺, where ionization and recombination occur at the same rate.
Want more questions with answers?Get the full practice set for this chapter.
What is the difference between homogeneous and heterogeneous equilibrium?
Homogeneous equilibrium involves all reactants and products in the same phase, while heterogeneous equilibrium involves reactants and products in different phases.
How does Le Chatelier's principle predict the direction of a reaction?
Le Chatelier's principle states that a system at equilibrium will adjust to counteract any changes in concentration, pressure, or temperature, thereby predicting the direction of the reaction.
What is the role of a catalyst in a chemical reaction?
A catalyst increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy, but it does not affect the equilibrium position.
What is the difference between the Arrhenius, Brönsted-Lowry, and Lewis theories of acids and bases?
The Arrhenius theory defines acids as substances that produce H+ ions in water and bases as substances that produce OH- ions. The Brönsted-Lowry theory defines acids as proton donors and bases as proton acceptors. The Lewis theory defines acids as electron pair acceptors and bases as electron pair donors.
What is the common ion effect?
The common ion effect is the decrease in solubility of a sparingly soluble compound in the presence of a common ion, due to the shift in equilibrium towards the formation of the less soluble compound.