R-ATCHE-9

Preface

We want:

• High yield (large % of products compared to reactants)
• Fast rate of attainment of desired product(do we say equi? good q for teacher :))
• Safety and product considerations

Rate:

• High temperature
• High pressure (for gasses)(higher concentration of reactants)
• Use suitable catalyst (as is not consumed in reaction, i.e. free money)

Yield:

• Le Chatelier
• e.g. Exo reaction favoured by low temperature - this is a contradiction, hence we need to find a compromise.
• Gasses
  • $Low \ mol \rightleftharpoons High \ mol$
  • Forward favoured by low pressure
  • Also a contradiction

Contact process and Haber process are important for assessments.

We won't need to know like how the factory is structured, none of that non-chem stuff >:(

BUT: We must remember key details

• Temp
• Pressure
• Catalyst

Haber Process

$N_{2(g)}+3H_{2(g)}\rightleftharpoons 2NH_{3(g)} \ \ \Delta H= -92kJ$

(To get high x):

• Rate
  • High pressure (lots of $N_{2}$ and $H_{2}$ per unit volume)
  • High temperature
  • Catalyst (for haber process, we use an iron oxide! ($Fe_{2}O_{3}$ OR $Fe_{3}O_{4}$))
• Yield
  • High pressure (Reaction moles: 4 moles $\to$ 2 moles, so forward reaction favoured)
  • Low temperature - because reaction is exothermic
  • Catalyst (same as before)

Conditions:

• High pressure (Not to high, cause of safety and operation costs)
  • Around 100-250atm
• Temperature will have to be a compromise
  • $350 \degree C - 550 \degree C$
  • Reasonable rate and yield
  • If the temperature is too low, the rate is too small.
  • If the temperature is too high, the yield is too low, i.e. we don't produce as much $NH_{3}$. Not poggies.
• We remove $NH_{3}$ as reaction proceeds
  • This means $NH_{3}$ is constantly being removed as it is produced, i.e. we are preventing the system from reaching equilibrium so the forward reaction is favoured
    • See Le Chat prediction when we reduce concentration of product
  • Even though it never reaches equilibrium, the yield argument still holds!!
    • Dunno why it wouldn't but Norrie said so so it must be true

Contact Process

A method of manufacturing sulfuric acid

Luckily, we consume $SO_{2}$, which is a stinky greenhouse gas. Good stuff.

This process is used to capture $SO_{2}$ and fix climate change!! WOo!!! (also sulfuric acid good product)

Factors increasing rate:

• High temperature
• High pressure
• Catalyst

Factors increasing yield:

• Lower temperature, because the reaction is exothermic.
• High pressure

i.e. same arguments as the Haber process!

Conditions:

• Pressure

  • Around 1-2atm
  • This is a little weird. Why such a low pressure compared to Haber? Because its really god damn expensive to maintain high pressures for this reaction. Costs are bad. Money makes the world go round(or so my father says)
  • "Benefits of high pressure outweighed by costs associated"

• Temperature will have to be a compromise

  • $450 \degree C$

• Catalyst

  • $V_{2}O_{5}$

• We remove $NH_{3}$ as reaction proceeds

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