AS/A-Level Chemistry - Catalytic activity questions

Let's work on some questions about catalysts in A-Level Chemistry to consolidate your learning!😏😏

1. Explain how catalysts work

• Provides an alternative route
• Lower activation energy E_a
• Speeds up reaction rate without being chemically changed or used up

2. Explain why transition metals are able to act as catalysts whereas non-transition metals are not usually able to act as catalysts

• Transition metals have variable oxidation states
• Non-transition metals only exist in one oxidation state

3. State the definition of a heterogeneous catalyst and homogeneous catalyst

• Heterogeneous catalyst is a catalyst in a different phase from the reactants
• Homogeneous catalyst is a catalyst in the same phase as the reactants

4. Explain how heterogeneous catalysts work

• Active sites where reactants are adsorbed onto the surface of the catalyst
• Where products are desorbed from the surface of the catalyst

5. State the equation, catalyst and poisonin the reaction in a catalytic converter

• 2CO + 2NO ⇨ 2CO₂+ N₂
• Catalyst is platinum, rhodium, palladium
• Poison is lead

6. Explain how and why the efficiency of the catalyst is increased in a catalytic converter

• Deposit catalyst on ceramic honeycomb
• Increases surface area
• Speeds up reaction between CO and NO
• Minimises cost

7. State the equation, catalyst and poison in the reaction in the Haber Process

• N₂ + 3H₂ ⇨ 2NH₃
• Catalyst is iron
• Poison is sulfur compounds

8. Explain how and why the efficiency of the catalyst is increased in the Haber Process

• Powder catalyst into granules
• Increase surface area
• Speed up reaction between N₂ and H₂
• Minimise cost

9. Explain why the efficiency of a heterogeneous catalyst may decrease and how the efficiency of the catalyst may be increased

• Poison species is adsorbed onto the surface of the catalyst, blocks the active site
• Poison species is not desorbed form the surface of the catalyst
• Purify reactants, remove poison species

10. State the catalyst in the reaction in the Contact Process and write an overall equation and the catalyticmechanisms for the reaction

• Catalyst is V₂O₅
• 2SO₂+ O₂ ⇨ 2SO₃
• V₂O₅+ SO₂ ⇨ V₂O₄+ SO₃
• 2V₂O₄+ O₂ ⇨ 2V₂O₅

11. State the catalyst in the reaction in the manufacture of methanol from carbon monoxide and hydrogen and write an overall equation for the reaction

• Catalyst is Cr₂O₃
• CO + 2H₂ ⇨ CH₃OH

12. Explain why the reaction between I^- and S₂O₈^2- is slow, state the catalyst in the reaction write an overall equation and the catalytic mechanisms for the reaction

• Both ions are negatively charged, repel each other
• High activation energy E_a
• Catalyst is Fe²⁺
• 2I^- + S₂O₈^2- ⇨ I₂+ 2SO₄^2-
• 2Fe²⁺+ S₂O₈^2- ⇨ 2Fe³⁺+ 2SO₄^2-
• 2Fe³⁺+ 2I^- ⇨ 2Fe²⁺+ I₂

13. Explain why the initial reaction between MnO₄^-  and C₂O₄^2-   is slow, state the catalyst in the reaction write an overall equation and the catalytic mechanisms for the reaction

• Both ions are negatively charged, repel each other
• High activation energy Ea
• Catalyst is Mn²⁺
• 2MnO₄^-+ 5C₂O₄^2-+ 16H⁺ ⇨2Mn²⁺+ 10CO₂+ 8H₂O
• 4Mn²⁺+ MnO^4-+ 8H⁺ ⇨ 5Mn³⁺+ 4H₂O
• 2Mn³⁺+ C₂O₄^2- ⇨ 2Mn²⁺+ 2CO₂

14. Explain the use of [Ag(NH₃)₂]⁺ and write an equation and observations for the reactions with propanal and propanone using [O] to represent the oxidising agent

• [Ag(NH₃)₂]⁺is used in Tollens’ reagent
• CH₃CH₂CHO + [O] ⇨ CH₃CH₂COOH
• Aldehyde shows colourless solution to form silver mirror
• Ketone shows no visible change, remains colourless solution

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Drafted by Eunice (Chemistry)

References:

• https://www.aa1car.com/library/converter.htm
• https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c6-nitrogen-and-phosphorus/haber-process.html
• https://mogckchem.weebly.com/the-contact-process-in-the-manufacture-of-sulfuric-acid.html
• https://everythingdynamicequilibrium.weebly.com/methanol-production.html
• https://www.sciencephoto.com/media/4204/view/silver-mirror-test