# Equilibrium Notes, Class 11 Chemistry | SwaVid Equilibrium, NCERT Class 11 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/chemistry/chapter/equilibrium Source: https://www.swavid.com/cbse/class-11/chemistry/chapter/equilibrium # Equilibrium ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Chemistry on SwaVid ### Dynamic nature of equilibrium ### Law of chemical equilibrium ### Le Chatelier's principle ### Ionic equilibrium and pH scale ### Buffer solutions and common ion effect ### Solubility product ### Next chapter ### Related chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Chemistry › Equilibrium Notes written by SwaVid from the NCERT textbook. Class 11 Chemistry, Unit 6. Key ideas, formulas and common mistakes. CBSE prints 7 marks for Unit 6, not for this chapter alone. Short answer. This chapter explains dynamic equilibrium in physical and chemical processes along with the quantitative laws governing it. Students learn how to calculate equilibrium constants, predict reaction shifts using Le Chatelier's principle, and analyse ionic balances involving acids, bases, and sparingly soluble salts. Source: NCERT Chemistry Part I (Reprint 2026-27) , Unit 6, Equilibrium Equilibrium in physical and chemical processes is reached when the rates of the forward and reverse processes become equal. The concentrations of reactants and products remain constant over time even though both reactions continue to occur at the molecular level. For a reversible reaction, the equilibrium constant Kc is the product of the equilibrium concentrations of products raised to their stoichiometric coefficients divided by that of reactants. For gaseous systems, Kp is expressed using partial pressures, linked by Kp = Kc (RT)^(Δn). If a system at equilibrium is subjected to a change in concentration, pressure, or temperature, the equilibrium shifts in the direction that tends to counteract the effect of the change. Adding a catalyst or an inert gas at constant volume does not shift the equilibrium position. Electrolytes ionise in water to form ions, creating an equilibrium between un-ionised molecules and ions. The acidity or basicity of an aqueous solution is represented on the pH scale, where pH = -log₁₀[H⁺] and pH + pOH = 14 at 298 K. The suppression of the ionisation of a weak electrolyte by the addition of a strong electrolyte containing a common ion is called the common ion effect. Buffer solutions resist drastic changes in pH upon the addition of small amounts of strong acid or base. For a sparingly soluble salt, the solubility product Ksp represents the product of the concentrations of its constituent ions in a saturated solution, each raised to the appropriate power. Precipitation occurs only when the ionic product Qsp exceeds Ksp. Try each question first. Then tap it to see the answer. Δn = moles of gaseous products - moles of gaseous reactants = 2 - (1 + 3) = -2 Kp = Kc (R T)^(Δn) = 0.50 × (0.0821 × 400)⁻² R T = 32.84 Kp = 0.50 / (32.84)² = 0.50 / 1078.47 = 4.64 × 10⁻⁴ 4.64 × 10⁻⁴ (or 4.64 × 10⁻⁴ atm⁻²) Ba(OH)₂ → Ba²⁺ + 2 OH⁻ [OH⁻] = 2 × 0.005 M = 0.01 M = 10⁻² M pOH = -log₁₀[OH⁻] = -log₁₀(10⁻²) = 2 pH = 14 - pOH = 14 - 2 = 12 12 AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq) [Ag⁺] = S and [Cl⁻] = S, so Ksp = S² Ksp = (1.05 × 10⁻⁵)² = 1.10 × 10⁻¹⁰ 1.10 × 10⁻¹⁰ Redox Reactions . Thermodynamics . Chemical Bonding and Molecular Structure . The 9 chapters of Class 11 Chemistry . CBSE does not give marks to one chapter. It prints 7 marks for Unit 6, Equilibrium, which includes Equilibrium. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Redox Reactions. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Unit 6 NCERT book - 7 marks, Unit 6 - 3 quick checks - Including pure solids and pure liquids in the equilibrium constant expression . Omit pure solids and pure liquids from Kc and Kp expressions because their molar concentrations or active masses remain constant and are incorporated into the constant itself. - Believing a catalyst increases the yield of products or shifts the equilibrium . A catalyst increases the rates of both forward and backward reactions equally. It helps the system attain equilibrium faster without changing the equilibrium composition or the value of K. - Calculating the pH of extremely dilute strong acid solutions as greater than 7 . When the acid concentration is 10⁻⁷ M or lower, add the contribution of H⁺ from the autoionisation of water instead of taking only the acid concentration. - Confusing reaction quotient Q with equilibrium constant K . Calculate Q using non-equilibrium concentrations at any given point in time. Compare Q with K: if Q K it moves backward, and if Q = K the system is at equilibrium. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 11](https://www.swavid.com/cbse/class-11) - [Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup) - [All 9 chapters](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [NCERT Chemistry Part I (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/redox-reactions) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/thermodynamics) - [Open notes](https://www.swavid.com/cbse/class-11/chemistry/chapter/chemical-bonding-and-molecular-structure) - [Class 11 Chemistry](https://www.swavid.com/cbse/class-11/chemistry/chapters) - [Start free →](https://www.swavid.com/signup)