Chemical eqm: Haber Process

Question 1

3 factors to maximise amt of product

Answer 1

• yield of product (amt formed)
• rate of reaction
• cost of maintaining reaction conditions

Question 2

Define Haber Process

Answer 2

• N2 (g) + 3H2 (g) 2NH3 (g)
• impt in the manufacture of ammonia
• nitrogen extracted from air using fractional distillation of liquid air
• hydrogen produced from cracking of petroleum
• reversible reaction,
• reaction conditions must be controlled
• achieve maximum yield of ammonia at min cost

Question 3

Temperature condition

Answer 3

• forward reaction is exothermic (enthalpy = -92 kJ/mol)
• lower temp favours forward reaction
• maximises yield of ammonia

Question 4

Pressure condition

Answer 4

• forward reaction produce 2 mol of gas
• backward reaction produce 4 mol of gas
• raising pressure maximises ammonia yield
• favours forward rxn

Question 5

Compromise between yield and rate of reaction

Answer 5

• high temp increase kinetic energy of molecules, hgher frequency of successful collisions
• low temp results in slow rate
• forward rxn exo, low temp favoured, high temp tends to drive backward rxn, less ammonia yield
• compromise of 450°c ensure reasonable yield for production of ammonia
• finely powdered iron used as catalyst

Question 6

Compromise between yield and cost

Answer 6

• higher pressure brings molecules closer tgt, faster rate of rxn
• greater yield of ammonia since right side lesser molecules
• chemical equipment that withstand high pressures expensive to build, require lots of energy to maintain
• med pressure of 200-250 atm, produce reasonable yield
• removing ammonia encourage forward reaction

Question 7

Industrial conditions for opt yield and rate of ammonia production

Answer 7

• temp: 450-500
• pressure: 200-250atm
• finely divided iron catalyst
• removal of ammonia is favourable to forward rxn

Question 8

Steps (6)

Answer 8

1. N2 and H2 mixed in ratio of 3:1
2. mixture of gases compressed to 200-300 atm (in compressor)
3. gases passed over finely-divided iron at 450 degrees and 250 atm ( in converter)
4. only abt 10-15% of N2 and H2 combine to form ammonia, mixture of all 3 leaves converter
5. mixture of gases is cooled, ammonia condenses to form liquid ammonia (in condenser)
6. unreacted N2 and H2 pumped back into converter for further rxn /recycled until used up

Question 9

Ammonia condensation

Answer 9

• condenses at 33 degrees

- N2 ad H2 condenses at lower temps

Question 10

Properties of ammonia

Answer 10

• colourless
• pungent smell
• alkaline (turns pH paper blue)
• very soluble in water, collect using downward displacement

Question 11

Ammonium hydroxide

Answer 11

• aqueous ammonia

- ammonia soln

Question 12

Uses of ammonia

Answer 12

• most ammonia converted to fertilisers
• provide nitrogen for plants
• achieved by reacting with acids
• make nitric acid,
• fibres and plastics (rayon, nylon)
• household cleaners

Question 13

Lab preparation of ammonia

Answer 13

• heating ammonium chloride (or other ammonium salts

- with sodium hydroxide (or other alkalis)

Question 14

Adding calcium hydroxide to soil

Answer 14

• farmers do this to remove acidity frm soil (e.g. acid rain)
• not advisable to add calcium hydroxide at the same time as ammonium nitrate
• ammonia gas formed will escape to surroundings
• loss of nitrogen to soil