Two-step mechanism: the slow step decides the rateदो-पद क्रियाविधि: धीमा पद वेग तय करता हैTwo-step mechanism: the slow step decides the rate
Class 12 Chemistry · Chapter 3 · interactive diagram
Parts and what they mean
- Energy path of 2H₂O₂ → 2H₂O + O₂ (catalysed by I⁻, alkaline medium) (2H₂O₂ → 2H₂O + O₂ का ऊर्जा पथ (I⁻ उत्प्रेरित, क्षारीय माध्यम)) — Two hills = two elementary steps. Both steps are bimolecular.
- Step 1: H₂O₂ + I⁻ → H₂O + IO⁻ (slow) (पद 1: H₂O₂ + I⁻ → H₂O + IO⁻ (धीमा)) — Highest barrier, so slowest. It is the rate determining step: Rate = k[H₂O₂][I⁻], first order in each.
- Step 2: H₂O₂ + IO⁻ → H₂O + I⁻ + O₂ (fast) (पद 2: H₂O₂ + IO⁻ → H₂O + I⁻ + O₂ (तेज़)) — Lower barrier. I⁻ comes back here, so it is a catalyst.
- IO⁻ — intermediate (IO⁻ — मध्यवर्ती) — Formed in step 1 and used up in step 2; it does not appear in the overall balanced equation.
- Ea1 — activation energy of step 1 (larger) (Ea1 — पद 1 की सक्रियण ऊर्जा (अधिक)) — Larger activation energy → smaller rate constant → slow step.
- Ea2 — activation energy of step 2 (smaller) (Ea2 — पद 2 की सक्रियण ऊर्जा (कम)) — Smaller barrier → fast step.
- Reactants: H₂O₂ with I⁻ catalyst (अभिकारक: H₂O₂ और उत्प्रेरक I⁻) — Overall: 2H₂O₂ → 2H₂O + O₂.
- Products: water and oxygen; I⁻ regenerated (उत्पाद: जल और ऑक्सीजन; I⁻ पुनः प्राप्त) — Products lie lower in energy: the decomposition of H₂O₂ is exothermic.
- Potential energy vs reaction coordinate (स्थितिज ऊर्जा बनाम अभिक्रिया निर्देशांक) — Like a relay race: the team is only as fast as its slowest runner.
Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake