Equilibrium Constants & Le Chatelier's Principle
Chemical Equilibrium represents a state where the rates of forward and backward reactions are equal. Mastering $K_c$, $K_p$, and the factors affecting equilibrium shifts is essential for Physical Chemistry in JEE and NEET.
1. Law of Mass Action & Equilibrium Constants
For a reversible reaction $aA + bB \rightleftharpoons cC + dD$, the equilibrium constant depends on the active mass (concentration) or partial pressure of the reactants and products.
If $\Delta n_g = 0$, then $K_p = K_c$. If $\Delta n_g > 0$, $K_p > K_c$.
Key Concept: Temperature Dependence
The value of the Equilibrium Constant ($K$) changes only with Temperature. It remains unaffected by changes in concentration, pressure, catalyst, or addition of inert gas.
Figure: Comprehensive Chart of Equilibrium Concepts and Le Chatelier's Principle
2. Le Chatelier's Principle
This principle predicts the direction in which an equilibrium will shift to counteract any change in conditions (concentration, pressure, or temperature).
Shift Rules
- Concentration: Adding reactant shifts equilibrium forward; removing product shifts it forward.
- Pressure: Increasing pressure shifts equilibrium towards fewer moles of gas.
- Temperature:
- Exothermic ($\Delta H < 0$): Low T favors forward reaction.
- Endothermic ($\Delta H > 0$): High T favors forward reaction.
3. Ionic Equilibrium (Acids & Bases)
Equilibrium concepts apply to the dissociation of weak acids and bases, buffer solutions, and solubility products.
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