Chapter 19: Ammonia Flashcards
Define reversible reactions.
A reversible reaction can go both forward and backward at the same time.
State an example of a reversible reaction involving ammonia other than the Haber Process.
Ammonia gas and hydrogen chloride gas can react to form a white solid of ammonium chloride:
NH3 (g) + HCl (g) → NH4Cl (s)
Simultaneously, NH4Cl can also decompose on heating:
NH4Cl (s) → NH3 (g) + HCl (g)
How is ammonia manufactured industrially? State the chemical equation.
Ammonia is manufactured industrially by the Haber Process.
N2 (g) + 3H2 ↔ 2NH3 (g)
How are N2 and H2 obtained for the Haber process?
N2 is obtained by the fractional distillation of liquid air.
H2 is obtained by the catalytic cracking of long-chained hydrocarbons/ electrolysis of water.
Describe the forward reaction of the Haber process.
The forward reaction is an exothermic reaction as the energy absorbed to break the bonds in N2 and H2 is lesser than the energy released to form the bonds in NH3. (Delta H = -92.4 kJ/ mol)
How does the Haber process being a reversible reaction affect the reaction conditions?
Since it is a reversible reaction, reaction conditions must be controlled to achieve maximum yield of ammonia at minimum cost.
What are the various factors that affect the yield of ammonia, and what are their limitations?
Pressure:
- Increase in pressure increases % yield of ammonia
- However, high pressures → very costly to maintain the pressure (equipment)
Temperature:
- Decrease in temperature increases % yield of ammonia
- However, low temperatures → slow reaction
List the set of optimum conditions for the manufacture of ammonia.
1) 450 degrees Celsius
2) 250 atm
3) Finely divided iron catalyst (speed up reaction)
What percentage of the hydrogen and nitrogen during the Haber process is converted into ammonia? What action has to be taken as a result of this?
Only 10 - 15% of the hydrogen and nitrogen is converted into ammonia. Gaseous ammonia is then converted into liquid ammonia and collected via condensation. This is possible because ammonia has a higher b.p. than N2 and H2, and b.p. = c.p.
What is an application of ammonia in real life?
Ammonia is used to make fertilisers which are necessary for survival for 1/3 of the world’s population
List 3 common types of nitrogenous fertilisers
1) Ammonium nitrate, NH4NO3 (35% by mass of nitrogen)
2) Ammonium sulfate, (NH4)2SO4 (21.2% by mass of nitrogen)
3) Urea, CO(NH2)2 (Contains 46.7% by mass of nitrogen but less soluble in water)
Why do farmers try not to decrease acidity and provide nutrients at the same time?
Displacement of ammonia:
1) NH4Cl (aq) + NaOH (aq) → NH3 (g) + H2O (l) + NaCl (aq)
2) 2NH4Cl (aq) + Ca(OH)2 (aq) → 2NH3 (g) + 2H2O (l) + CaCl2 (aq)
It involves the liberation of ammonia gas which contains a large percentage of nitrogen that is necessary for plant growth.
