--- title: "Catalysis, importance, intermediate compound theory" subject: "Engineering Chemistry" chapter: 2 key: "semester_2/engineering_chemistry:catalysis-importance-intermediate" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalysis-importance-intermediate site: BCT Engineering --- # Catalysis, importance, intermediate compound theory Engineering Chemistry · Chapter 2: Catalyst - Asked in: 2068 Bhadra, 1+1+3 marks - Video: [Theory of intermediate compound formation and Adsorption theory | Theories of catalysis](https://www.youtube.com/watch?v=b7LqVwlpHts) — Chemistry Scholars - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalysis-importance-intermediate - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-2 ## Question What is meant by catalysis? Point out its importance. Discuss intermediate compound formation theory of catalysis with suitable examples. ## Short answer Catalysis is the change of reaction rate by a substance not consumed, vital for industrial processes like ammonia and sulfuric acid manufacture, enabling lower energy use. The intermediate theory explains it through unstable compounds regenerating the catalyst, exemplified by NO in the lead chamber process and V₂O₅ in the contact process. ## Answer #### Catalysis A **catalyst** is a substance that changes the rate of a chemical reaction without being consumed in the reaction (its mass and chemical nature are the same at the end). The phenomenon is called **catalysis**. Example: MnO₂ speeds up the decomposition of KClO₃ to O₂. #### Importance of catalysis - Manufacture of ammonia (Fe, Haber), H₂SO₄ (V₂O₅, contact), HNO₃ (Pt, Ostwald) and methanol. - Hydrogenation of vegetable oils to ghee (Ni). - Petroleum cracking and reforming (zeolites, Pt). - Control of vehicle pollution: catalytic converters with Pt/Pd/Rh. - Biological systems: enzymes catalyse digestion and metabolism. - Catalysts allow lower temperature and pressure, saving fuel and cost, and give better yields. #### Intermediate compound formation theory According to the **intermediate compound formation theory**, the catalyst takes part in the reaction by forming an unstable intermediate compound with one of the reactants. The intermediate has a lower activation energy path and reacts with the other reactant to give the product and regenerate the catalyst. ```text Uncatalysed: A + B ───────────→ AB (high Ea) Catalysed : A + C → [AC] (fast, low Ea) [AC] + B → AB + C (fast, low Ea) (C = catalyst, regenerated) ``` **Examples** 1. Lead chamber process (NO as catalyst): 2NO + O₂ → 2NO₂ (intermediate) NO₂ + SO₂ → SO₃ + NO (catalyst regenerated) 2. Preparation of diethyl ether from ethanol with conc. H₂SO₄: C₂H₅OH + H₂SO₄ → C₂H₅HSO₄ (ethyl hydrogen sulphate) + H₂O C₂H₅HSO₄ + C₂H₅OH → C₂H₅OC₂H₅ + H₂SO₄ 3. Contact process with V₂O₅: V₂O₅ + SO₂ → V₂O₄ + SO₃, then V₂O₄ + ½O₂ → V₂O₅. **Limitation:** it explains homogeneous catalysis well, but is not suitable for many heterogeneous cases where no stable intermediate is found. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A catalyst is a substance that: A. Changes the rate of a reaction without being consumed B. Is consumed to form the product C. Changes only the equilibrium constant D. Always increases the rate Answer: A. A catalyst's mass and chemical nature are the same at the end; catalysts can also slow reactions (negative). (Key point: Catalyst definition) 2. Which pair is a correct industrial use of a catalyst? A. Fe in ammonia manufacture; Pt in nitric acid (Ostwald) process B. Ni in ammonia manufacture; Fe in ghee C. Pt in Haber's process; V2O5 in ghee D. V2O5 in nitric acid; Fe in sulphuric acid Answer: A. Fe for NH3, V2O5 for H2SO4, Pt for HNO3, Ni for hydrogenation to ghee. (Key point: Importance of catalysis) 3. According to the intermediate compound formation theory, the catalyst: A. Adsorbs all reactants permanently on its surface B. Is used up completely forming the product C. Forms an unstable intermediate with a reactant, which reacts further and regenerates the catalyst D. Only raises the temperature of the reaction Answer: C. The intermediate provides a lower-Ea path and releases the catalyst again when the product forms. (Key point: Intermediate compound theory) 4. In the V2O5 catalysed contact process, V2O5 first reacts with SO2 to form: A. V2O3 and SO2 permanently B. VO and SO4 C. V2O4 and SO3, then V2O4 is re-oxidised to V2O5 D. V2O5 is never changed Answer: C. V2O5 + SO2 -> V2O4 + SO3, then V2O4 + 1/2 O2 -> V2O5, regenerating the catalyst. 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