Cambridge IGCS Chemistry Coursebook 2023 Chapter 9 知识点整理

这是一篇关于Reversible reactions and equil的思维导图，主要内容包括：Reversible reactions，Fertilisers，Haber process and Contact proces。

Reversible reactions and equilibrium

• Haber process and Contact proces
  • Haber process
    • Fertiliser: a substance added to the soil to replace essential elements lost when crops are harvested, which enables crops to grow faster and increases the yield.
    • Conditions for the Haber process
      • compromise temperature: a temperature that gives sufficient product and a reasonable and economic rate of reaction
      • N2(g) + 3H2(g) ⇌ 2NH3(g)
        • Pressure
          • 4 moles ⇌ 2 moles
        • Temperature
          • exothermic ->
          • endothermic <-
        • Catalyst
      • • N2 and H2 are mixed in a ratio of 1:3 • an optimum (or compromise) temperature of 450 °C • a pressure of 20 000 kPa (200 atmospheres) • a catalyst of finely divided iron.
    • Industrial plant for the Haber process
      • CH4(g) + H2o(g) → CO(g) + 3H2(g)
      • CO(g) + H2O(g) → CO(g) + H2(g)
      • C2H6(g) → C2H4(g) + H2(g)
  • Contact process
    • Conditions for the Contact process
      • 2SO2(g) + O2(g) ⇌ 2SO3(g)
        • exothermic (ΔH = -197 kJ / mol )
      • • a compromise (optimum) temperature of about 450°C • a catalyst of vanadium(V) oxide (V2O5) • an operating pressure of 200 kPa.
    • Industrial plant for the Contact process
      • Desulfurisation: an industrial process for removing contaminating sulfur from fossil fuels such as petrol (gasoline) or diesel
      • S(s) + O2(g) → SO2(g)
      • 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
      • 2SO2(g) + O2(g) → 2SO3(g)
      • SO3 + H2O → H2SO4
      • SO3 + H2 SO4 → H2S2O7
• Fertilisers
  • NH3(aq) + HNO3(aq) → NH4NO3(aq)
  • • phosphorus (P), especially important for healthy roots • potassium (K), which is important for the production of flowers and fruit.
  • • Straight N fertilisers are solid nitrogen-containing fertilisers sold in pellet form, for example, ammonium nitrate (NH4NO3), ammonium sulfate (NH4)2SO4) and urea (CO(NH2)2)
  • • NPK compound fertilisers are mixtures that supply the three most essential elements lost from the soil by extensive use: nitrogen (N), phosphorus (P) and potassium (K). They are usually a mixture of ammonium nitrate, ammonium phosphate and potassium chloride, in different proportions to suit different conditions. The numbers on a bag of NPK fertiliser correspond to the percentage of that nutrient in the make-up of the fertiliser, e.g. 21:8:11 indicates 21% nitrogen, 8% phosphorus and 11% nitrogen, with the remaining 60% being filler ingredients that help disperse the chemicals. Nitrogen is sometimes omitted from these fertilisers because it washes into streams and rivers causing algal growth.
  • Compound fertiliser: a fertiliser such as an NPK fertiliser or nitrochalk that contains more than one compound to provide elements to the soil
  • NPK fertiliser: fertilisers to provide the elements nitrogen, phosphorus and potassium for improved plant growth
• Reversible reactions
  • Reversible hydration of salts
    • CuSO4 · 5H20(s) ⇌ CuSO4(s) + 5H2O(g)
      • light blue crystals ⇌ white powder
    • CoCL2 · 6H20 ⇌ CoCl2 + 6H2O
      • pink ⇌ blue
    • Chemical test for the presence of water
  • Chemical equilibria
    • Closed system: a system where none of the reactants or products can escape the reaction mixture or the container where the reaction is taking place
    • Dynamic (chemical) equilibrium: two chemical reactions, one the reverse of the other, taking place at the same time, where the concentrations of the reactants and products remain constant because the rate at which the forward reaction occurs is the same as that of the reverse reaction
    • • It is dynamic: reactants are continuously being changed to products and products are continuously being changed back to reactants. • The forward and reverse (backward) reactions occur at the same rate. • The concentrations of reactants and products (the position of equilibrium) remain constant. • It requires a closed system.
  • Chemical equilibria and reaction conditions
    • Contact process: the industrial manufacture of sulfuric acid using the raw materials sulfur and air
    • Temperature: Increasing the temperature makes the reaction move in the direction that takes in heat (the endothermic direction). Decreasing the temperature makes the reaction move in the direction that gives out heat (the exothermic direction).
    • Pressure: This only affects reactions involving gases. Increasing the pressure shifts the equilibrium in the direction that produces fewer gas molecules. Decreasing the pressure shifts the equilibrium in the direction that produces more gas molecules.
    • Concentration: Increasing the concentration of one substance in the mixture makes the equilibrium move in the direction that produces less of that substance. Decreasing the concentration of one substance in the mixture makes the equilibrium move in the direction that produces more of that substance.
    • Catalyst: Using a catalyst does not affect the position of equilibrium, but the reaction reaches equilibrium faster.
  • Reversible reaction: a chemical reaction that can go either forwards or backwards, depending on the conditions
  • hydrated salts: salts whose crystals contain combined water (water of crystallisation) as part of the structure
  • Anhydrous: an adjective to describe a substance without water combined with it