NCERT Class 11 Chemistry Chemistry Part-I: Chapter 6 — Equilibrium
This chapter, Equilibrium, from NCERT Class 11 Chemistry Part-I, introduces the concept of chemical equilibria and their significance in biological and environmental processes. It explains the dynamic nature of equilibrium in both physical and chemical processes, including solid-liquid and liquid-vapor equilibria. The chapter details the law of equilibrium, equilibrium constant expressions (Kc and Kp), and factors affecting equilibrium. It also delves into ionic equilibrium, covering Arrhenius, Bronsted-Lowry, and Lewis acid-base concepts, ionization constants, the pH scale, ionic product of water, buffer solutions, and solubility product constant. Understanding these principles is crucial for predicting reaction outcomes and optimizing conditions in various applications, aiding students in their CBSE Chemistry learning.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Chemistry |
| Book | Chemistry Part-I |
| Chapter | Chapter 6 — Equilibrium |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 6 minutes |
| Word count | 1090 |
Learning outcomes
- Identify the dynamic nature of equilibrium in physical and chemical processes.
- State and explain the law of equilibrium and its characteristics.
- Write expressions for equilibrium constants (Kc and Kp) and establish their relationship.
- Explain factors affecting equilibrium and classify acids/bases using different concepts.
- Describe the pH scale, ionic product of water, buffer solutions, and solubility product.
Vocabulary
| Word | Meaning |
|---|---|
| Equilibrium | A state where forward and reverse reaction rates are equal, resulting in no net change in concentrations. |
| Dynamic Equilibrium | Equilibrium where opposing processes occur continuously at equal rates. |
| Equilibrium Constant | A ratio of product concentrations to reactant concentrations at equilibrium, raised to stoichiometric powers. |
| Kp | Equilibrium constant expressed in terms of partial pressures. |
| Kc | Equilibrium constant expressed in terms of molar concentrations. |
| Arrhenius Concept | Acids produce H+ ions in water; bases produce OH- ions. |
| Bronsted-Lowry Concept | Acids are proton donors; bases are proton acceptors. |
| Lewis Concept | Acids are electron-pair acceptors; bases are electron-pair donors. |
| pH | A measure of the acidity or alkalinity of a solution, based on hydrogen ion concentration. |
| Buffer Solution | A solution that resists changes in pH when small amounts of acid or base are added. |
| Solubility Product Constant | The product of the concentrations of ions in a saturated solution of a sparingly soluble salt. |
| Ionic Equilibrium | Equilibrium involving ions in aqueous solutions. |
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Practice questions
- What is the difference between static and dynamic equilibrium? Answer: Static equilibrium involves no movement, while dynamic equilibrium involves continuous opposing processes occurring at equal rates.
- Define the equilibrium constant Kc. Answer: Kc is the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of its stoichiometric coefficient.
- State the Bronsted-Lowry definition of an acid and a base. Answer: An acid is a proton donor, and a base is a proton acceptor.
- What is the pH scale used for? Answer: The pH scale is used to represent the hydrogen ion concentration in a solution, indicating its acidity or alkalinity.
- What is a buffer solution? Answer: A buffer solution resists changes in pH upon addition of small amounts of acid or base.
Frequently asked questions
What is chemical equilibrium?
Chemical equilibrium is a state in a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the concentrations of reactants and products.
What is the difference between Kc and Kp?
Kc is the equilibrium constant expressed in terms of molar concentrations, while Kp is the equilibrium constant expressed in terms of partial pressures of gaseous reactants and products.
What are the three concepts for classifying acids and bases?
The three concepts are Arrhenius, Bronsted-Lowry, and Lewis concepts.
How is the pH scale used?
The pH scale measures the acidity or alkalinity of a solution, ranging from 0 (highly acidic) to 14 (highly alkaline), with 7 being neutral.
What is the role of a buffer solution?
A buffer solution helps maintain a stable pH by resisting significant changes when small amounts of acid or base are added.
What does the solubility product constant (Ksp) represent?
Ksp represents the equilibrium constant for the dissolution of a sparingly soluble ionic compound in water.
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NCERT Class 11 Chemistry — Chemistry Part-I — Chapter 6 — Equilibrium. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.