8.2.5The Periodic Table
Industrial Processes and Equilibrium — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 4 parts Lesson 10 of 23 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Balancing the Factors
Industrial conditions are a compromise, because the best yield is not always the best choice overall.
Yield
- Yield Low temperature and high pressure favour the exothermic Haber reaction and give a higher yield of ammonia.
Rate
- Rate A low temperature slows the reaction, so a compromise temperature is needed to produce product in a reasonable time.
Cost
- Cost High pressure requires strong, expensive equipment and more energy, which adds to the running cost.
Safety
- Safety High pressures are dangerous, so a pressure that is safe to handle is chosen.
Section 2 of 4Haber Process Conditions
The Haber process uses an iron catalyst at a compromise temperature and pressure.
1
The reaction is N₂(g) + 3H₂(g) ⇌ 2NH₃(g), and the forward reaction is exothermic.
2
A temperature of 450 °C is used, a compromise between a lower yield and a reasonable rate of reaction.
3
A pressure of about 200 atm is used, which gives a good yield without being too costly or unsafe.
4
Unreacted nitrogen and hydrogen are recycled, so the reactants are used efficiently.
Section 3 of 4Contact Process Conditions
The second stage of the Contact process is an equilibrium reaction.
Contact Process Conditions
Stage
- Stage Sulfur dioxide is oxidised to sulfur trioxide in a reversible reaction, using oxygen from the air.
Temperature
- Temperature About 450 °C is used, because the forward reaction is exothermic and a lower temperature would be too slow.
Pressure
- Pressure Only about 2 atm is used, because the yield is already high at this pressure and higher pressures are not worth the cost.
Catalyst
- Catalyst A vanadium(V) oxide catalyst speeds up the reaction without changing the position of equilibrium.
Section 4 of 4Exam Checklist & Tips
8.2.5 – Key Points for the Exam
- Yield The amount of product obtained from a reaction.
- Haber process The industrial manufacture of ammonia from nitrogen and hydrogen.
- Contact process The industrial manufacture of sulfuric acid from sulfur, oxygen and water.
- Recycling Returning unreacted reactants to the reaction vessel so they can react again.
Common Mistakes
- Saying the compromise temperature gives the highest yield;
- a lower temperature gives a higher yield but too slowly.
- Stating that a catalyst is used to increase the yield in the Haber process;
- a catalyst only increases the rate.
- Assuming the Contact process needs high pressure; the yield is already high at about 2 atm.
- Stating the conditions without explaining why a compromise is needed.
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