Understanding Dynamic Equilibrium in Chemical Reactions ⚖️

🌟 Key Characteristics of ALL Equilibria (Physical & Chemical)

When a system reaches equilibrium:

  • 🔒 It must be a closed system at a fixed temperature.
  • ⚡ Both forward & reverse processes happen at the same speed (dynamic but stable!).
  • 📏 All measurable properties (like concentration, pressure, color) stay constant.
  • 📊 For physical processes, one parameter (e.g., vapor pressure) has a fixed value at a given temperature.

🧪 Chemical Equilibrium = Dynamic Balance 🔄

In reversible reactions like \( \ce{A + B <=> C + D} \):

  • ⏱️ Over time: Reactants (\(\ce{A, B}\)) decrease ⬇️, products (\(\ce{C, D}\)) increase ⬆️.
  • ⚖️ Forward reaction slows down, reverse reaction speeds up until rates become equal.
  • 🎯 At equilibrium: Concentrations stay constant (but reactions don’t stop!).

Graph showing concentrations stabilizing at equilibrium

🔬 Proof That Equilibrium is DYNAMIC (Not Static!)

Haber’s Process Experiment: Synthesis of ammonia (\(\ce{N2 + 3H2 <=> 2NH3}\))

  • 🧪 Scientists replaced \(\ce{H2}\) with deuterium (\(\ce{D2}\)) – its heavy isotope.
  • ⚗️ Both setups (\(\ce{H2/N2}\) and \(\ce{D2/N2}\)) reached identical equilibrium states (just \(\ce{NH3}\) vs. \(\ce{ND3}\)).
  • 🤯 When mixed: \(\ce{NH3}\), \(\ce{NH2D}\), \(\ce{NHD2}\), \(\ce{ND3}\) were found! Atoms swapped continuously even after equilibrium.
  • 💡 Conclusion: Forward/reverse reactions never stop – it’s dynamic!

🎮 Cool Activity to “See” Dynamic Equilibrium (Try This!)

Materials: 2 measuring cylinders, 2 glass tubes (3-5mm diameter), colored water (add KMnO4 💜).

Steps:

  1. Fill Cylinder-1 halfway with colored water. Leave Cylinder-2 empty.
  2. Use Tube-1 to transfer water from Cyl-1 → Cyl-2.
  3. Use Tube-2 to transfer water from Cyl-2 → Cyl-1.
  4. Repeat until water levels stop changing ⏹️.

Observation:

  • Levels become constant, but water keeps moving through tubes! 🔁
  • This mimics reactants ⇄ products: constant concentration but ongoing reactions.

Bonus: Try tubes of different diameters – equilibrium levels change! 🤓

🚀 NEET Super-Important Concepts 💡

  1. Dynamic ≠ Static: At equilibrium, reactions continue at equal forward/reverse rates. (No net change!)
  2. Equilibrium from Any Direction: Start with reactants OR products – you’ll reach the same equilibrium mixture! (e.g., \(\ce{H2 + I2 <=> 2HI}\) in Fig 6.5)
  3. Isotopes Reveal Dynamics: Deuterium experiments (like Haber’s) prove atoms keep exchanging.
  4. Constant Concentrations: Once equilibrium is hit, [reactants] and
    stay steady (but not equal!).