Class 10 Computer Science Chapter 1: Office Tools (Notes & Online Test) - PSEB

EQUILIBRIUM

NCERT Masterclass & NEET Study Module

1. Equilibrium in Physical and Chemical Processes

Equilibrium is a dynamic state where the rate of the forward reaction equals the rate of the backward reaction. At this stage, macroscopic properties (like concentration, pressure, color) become constant, but microscopic molecular activity continues.

2. Law of Chemical Equilibrium and Equilibrium Constant

For a general reversible reaction: $aA + bB \rightleftharpoons cC + dD$

$K_c = \frac{[C]^c [D]^d}{[A]^a [B]^b}$

Relation between $K_p$ and $K_c$:
$K_p = K_c (RT)^{\Delta n_g}$

Where $\Delta n_g$ = (moles of gaseous products) - (moles of gaseous reactants). Pure solids and pure liquids are ignored (active mass = 1).

Reaction Quotient ($Q_c$): It helps predict the direction of a reaction.

• If $Q_c > K_c$: Reaction proceeds backwards (towards reactants).
• If $Q_c < K_c$: Reaction proceeds forwards (towards products).
• If $Q_c = K_c$: Reaction is exactly at equilibrium.

3. Le Chatelier's Principle

If a change in concentration, temperature, pressure, or volume is imposed on a system at equilibrium, the system shifts in a direction that tends to counteract the change.

• Effect of Concentration: Adding reactants shifts equilibrium forward. Removing products shifts equilibrium forward.
• Effect of Pressure: Increasing pressure shifts equilibrium towards the side with fewer gaseous moles.
• Effect of Temperature: Increasing temperature favors the endothermic reaction direction. Decreasing temperature favors the exothermic direction.
• Effect of Inert Gas: At constant volume: No effect. At constant pressure: Shifts towards more gaseous moles.
• Effect of Catalyst: Does NOT alter the equilibrium state or $K_c$; it only helps achieve equilibrium faster.

4. Acids, Bases and pH Scale

Arrhenius Concept: Acids give $H^+$ in water, bases give $OH^-$ in water.
Brønsted-Lowry Concept: Acids are proton ($H^+$) donors, bases are proton acceptors.
Lewis Concept: Acids are electron-pair acceptors (e.g., $BF_3$), bases are electron-pair donors (e.g., $NH_3$).

Ionic Product of Water ($K_w$): $K_w = [H^+][OH^-] = 1.0 \times 10^{-14}$ at 298 K. As temperature increases, $K_w$ increases.

$$pH = -\log[H^+]$$
$$pH + pOH = 14$$

5. Buffer Solutions & Solubility Product ($K_{sp}$)

Buffer Solution: A solution that resists changes in pH upon the addition of small amounts of acid or base.

• Acidic Buffer: Weak acid + its salt with a strong base (e.g., $CH_3COOH + CH_3COONa$).
• Basic Buffer: Weak base + its salt with a strong acid (e.g., $NH_4OH + NH_4Cl$).

Henderson-Hasselbalch Equation: $pH = pK_a + \log\frac{[Salt]}{[Acid]}$

Solubility Product ($K_{sp}$): For a sparingly soluble salt $A_x B_y \rightleftharpoons xA^{y+} + yB^{x-}$, the $K_{sp} = [A^{y+}]^x [B^{x-}]^y$.
Precipitation Condition: A precipitate forms only when the Ionic Product ($Q_{sp}$) exceeds the Solubility Product ($K_{sp}$). i.e., $Q_{sp} > K_{sp}$.

Common Ion Effect: The solubility of a sparingly soluble salt decreases drastically upon the addition of a strong electrolyte having a common ion.

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🚀 NEET EQUILIBRIUM MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Le Chatelier's Principle, pH, Buffers and $K_{sp}$.

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