Ammonia Flashcards
What is a reversible reaction
A reversible reaction is a reaction that can go forwards or backwards depending on the conditions
What is the process of making ammonia called
Haber Process
How is hydrogen obtained for the Haber Process
Cracking of C18 alkane
- High pressure
- High temperature
- Catalyst
Reaction of methane with steam
- 30 atm
- 800 degrees Celsius
- Nickel oxide catalyst
What are the raw materials needed for the Haber Process
- Nitrogen
- Hydrogen
What are the optimal conditions for the Haber Process
- 200 atm
- 450 degrees Celsius
- Iron catalyst
How is nitrogen obtained for the Haber Process
Fractional distillation of liquid air
Describe the Haber Process
- Mixture of nitrogen and hydrogen in a 1:3 ratio is sent to compressor
- Gases are subjected to 200 atm pressure
- Pressurised gases then heated to 450 degrees Celsius and passed over finely divided iron catalyst in a convertor
- Nitrogen and hydrogen react on the iron’s surface to form ammonia
- Mixture of ammonia, hydrogen and nitrogen are cooled in the cooling chamber
- Only ammonia condenses to form liquid ammonia
- Unreacted gases pumped back to converter for further reaction
- Eventually about 98% of gases are converted to ammonia
State Le Chatelier’s Principle
Le Chatelier’s Principle states that if a system in equilibrium is subjected to a change, the system will respond in a way to counteract the change
Why is only 98% of the nitrogen and hydrogen converted to ammonia
- Reaction does not go to completion
- State of dynamic equilibrium is reached
- Speed of forward reaction equals speed of backward reaction
Why is 200 atm used in Haber Process
- According to le Chatelier’s Principle, reaction mixture will try to decrease pressure when pressure increases
- Forward reaction is favoured as it produces fewer molecules, allowing pressure to be lower
- High pressure required for high ammonia yield
- Expensive equipment is needed
- 200 atm selected as compromise
Why is 450 degrees Celsius used in the Haber Process
- Forward reaction is exothermic
- According to Le Chatelier’s Principle, reaction mixture will increase temperature when temperature decreases
- Forward reaction favoured as it releases heat
- Low temperature required for high ammonia yield
- Lower temperature results in slower reaction
- 450 degrees Celsius selected as compromise
