Chemistry Ammonia

• Chemical Reaction to produce Ammonia Gas in the Haber Process

  N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
• How is Ammonia produced?

  Heating of Ammonium Salts (eg. Ammonium Nitrate) with Alkali (aqueous base)
• Why is calcium hydroxide used ONLY AFTER SEVERAL DAYS as fertiliser to correct the pH of soil and improve soil fertility

  Ammonium salts will react with the calcium hydroxide to produce ammonia gas which Will be released into the environment. This reduces the amount of nitrogen (NH3 is released, less N in soil) in the soil required for plant growth.
• Heating of Ammonium Salts examples

  Ammonium Sulfate ⇌ Ammonia (g) + Sulfuric Acid (aq)

  Ammonium Chloride ⇌ Ammonia (g) + Hydrochloric Acid (aq)

  Ammonium Carbonate ⇌ Ammonia (g) + Carbon Dioxide (g) + Water

  [NOT Carbonic Acid]
• How is Nitrogen (N2) Gas obtained?

  Fractional Distillation of Liquid Air
• How is Hydrogen (H2) Gas obtained?

  Cracking of Crude Oil
• N2 and H2 are mixed in the ratio of…to produce how many moles of Ammonia Gas?

  1mol : 3moles…2moles
• Should the Haber Process be carried out at room temperature? Why?

  No. Nitrogen is inert (unreactive) at room temperature and pressure.
• Why should we use a catalyst in the Haber Process?


  As the process is still slow at higher temperatures and pressure, a catalyst should be used to speed up the reaction
• What are the optimal conditions for the Haber Process?

  Pressure: 250atm

  Temperature: 450 degree Celcius

  Presence of finely-divided iron catalyst
• How does the Haber Process work?

  N2 and H2 are mixed in the ratio of 1:3. The gas mixture is compressed to 250atm in a compressor and the compressed gas flows over to the iron catalyst where it is heated at 450 degrees Celcius in the catalyst chamber. ~15% of the N2 and H2 combine to form NH3. Unreacted N2 and H2 are recycled in the converter and the mixture of NH3, N2 and H2 are cooled in the cooling chamber. Ammonia gas condenses into liquid and pumped into the tank and stored under pressure.
• Percentage Yield = Actual Yield / Theoretical Yield x 100%

  (if they mention eg. : 10dm3 of H2 gas was formed, this is the actual yield)
• How is pressure and yield of ammonia related?

  Higher pressures = Higher yield of ammonia
• Why is it advisable not to use high pressures during the Haber Process?

  It is expensive to generate and maintain the high pressures and would require equipment that can withstand extreme pressures
• Relation between temperature and yield of ammonia?

  Higher temperature = Lower yield of ammonia

  This is due to thermal decomposition of NH3
• Why should a temperature of 450 degrees Celcius be used?

  At low temperatures, the Haber process would proceed too slowly. At high temperatures, NH3 will be decomposed to form N2 and H2 (opposite reaction)
• Effects of using a Catalyst on percentage yield

  no change in the yield of ammonia as catalysts only increase the rate of the reaction
• Percentage Purity = mass of pure substance / mass of impure substance x 100%
• What is a reversible reaction?


  It is a reaction that takes place in both directions.
• Use of Haber Process

  Manufacture ammonia