What is Le Chatelier's Principle?

When a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, it shifts in the direction that opposes the change and re-establishes equilibrium.

What is the difference between Kc and Kp?

Kc uses molar concentrations; Kp uses partial pressures. They are related by Kp = Kc(RT)^Δn where Δn is the difference in moles of gaseous products and reactants.

Why does a catalyst not shift equilibrium?

A catalyst speeds up both forward and backward reactions equally, so the equilibrium position (Kc) does not change — only the time to reach equilibrium decreases.

Chemical Equilibrium

Equilibrium • Class 11 Chemistry • NCERT • CBSE

At equilibrium, rates of forward and backward reactions are equal. Kc = [Products]/[Reactants]. Kp = Kc(RT)^Δn. Le Chatelier's Principle: system shifts to oppose any change. pH = −log[H⁺].

Key Formulas

Kc = [C]^c[D]^d / [A]^a[B]^b
Kp = Kc(RT)^Δn
pH = −log[H⁺]
pH + pOH = 14
Kw = [H⁺][OH⁻] = 10⁻¹⁴
pH = pKa + log([A⁻]/[HA]) (Henderson-Hasselbalch)

Frequently Asked Questions

What is Le Chatelier's Principle?: When a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, it shifts in the direction that opposes the change and re-establishes equilibrium.
What is the difference between Kc and Kp?: Kc uses molar concentrations; Kp uses partial pressures. They are related by Kp = Kc(RT)^Δn where Δn is the difference in moles of gaseous products and reactants.
Why does a catalyst not shift equilibrium?: A catalyst speeds up both forward and backward reactions equally, so the equilibrium position (Kc) does not change — only the time to reach equilibrium decreases.

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