Chemical Equilibrium

Chemical Equilibrium

Many chemical reactions do not go to completion but reach a state of dynamic equilibrium where the rate of the forward reaction equals the rate of the reverse reaction. This concept is critical in understanding environmental systems and industrial processes.

The Equilibrium Constant (KeqK_{eq})

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

The equilibrium constant expression is: Keq=[C]c[D]d[A]a[B]bK_{eq} = \frac{[C]^c [D]^d}{[A]^a [B]^b}

  • KcK_c: Uses molar concentrations.
  • KpK_p: Uses partial pressures (for gases).
  • Pure solids and liquids are omitted from the expression.

Le Chatelier's Principle

Le Chatelier's Principle

"If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change."

  • Concentration: Adding a reactant shifts equilibrium to the right (products).
  • Pressure: Increasing pressure shifts equilibrium to the side with fewer moles of gas.
  • Temperature: Depends on enthalpy. For exothermic reactions (ΔH<0\Delta H < 0), heat is a product; increasing T shifts left.

Acid-Base Equilibria

pH and pOH

  • pH: A measure of acidity. pH=−log⁡[H+]pH = -\log[H^+]
  • pOH: A measure of basicity. pOH=−log⁡[OH−]pOH = -\log[OH^-]
  • Relationship at 25∘^\circC: pH+pOH=14.00pH + pOH = 14.00
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