Class 11 Chemistry - ISC
Equilibrium
The Chapter 'Equilibrium' in Class 11 Chemistry explores reversible reactions where the rates of forward and backward reactions become equal. You will learn about chemical and ionic equilibria, Le Chatelier's principle, and how factors like temperature, pressure, and concentration shift equilibrium positions. A major focus is placed on acids, bases, salts, pH calculations, buffer solutions, and solubility product of sparingly soluble salts. This is a high-scoring physical chemistry chapter that is extremely important for your ISC board examinations and forms the foundational concept for advanced chemical thermodynamics and kinetics in Class 12.
Start Learning FreeKey Concepts
Dynamic Equilibrium
A state in a reversible reaction where the rate of the forward reaction equals the rate of the backward reaction, and macroscopic properties remain constant.
Law of Chemical Equilibrium and Equilibrium Constant
At a given temperature, the product of molar concentrations of products raised to their stoichiometric coefficients divided by reactants is a constant known as Kc or Kp.
Le Chatelier's Principle
If a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium shifts in a direction that tends to undo the effect of the change.
Ionic Equilibrium in Solutions
The equilibrium involving ions in aqueous solutions, governed by the ionization constants of weak acids (Ka) and weak bases (Kb), and the ionic product of water (Kw).
Buffer Solutions
Solutions that resist drastic changes in pH upon the addition of small amounts of a strong acid or a strong base.
Solubility Product (Ksp)
The product of the concentrations of ions in a saturated solution of a sparingly soluble salt at a given temperature, raised to the power of their stoichiometric coefficients.
Important Formulas
Board Exam Info
In the ISC Class 11 Chemistry examination, the Equilibrium chapter typically carries around 6 to 8 marks. Questions frequently include numerical problems on calculating pH, buffer action, relation between Kp and Kc, and applying Le Chatelier's principle to industrial processes like the Haber process.
Frequently Asked Questions
What is the difference between Kc and Kp?
Kc is the equilibrium constant expressed in terms of molar concentrations (mol/L), whereas Kp is expressed in terms of partial pressures of gases (atm or bar).
Why does a catalyst not change the equilibrium constant?
A catalyst speeds up both the forward and backward reactions to the exact same extent, helping the system reach equilibrium faster without altering the position of equilibrium or the value of K.
How do we know if a reaction will move forward or backward?
We calculate the reaction quotient (Qc or Qp) and compare it with the equilibrium constant (Kc or Kp). If Q < K, the reaction proceeds in the forward direction; if Q > K, it proceeds backward.
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