Dynamic Equilibria

Question 1

What is the Haber process?

Answer 1

A reversible reaction that forms ammonia

from nitrogen and hydrogen.

Question 2

Describe the steps that are carried out during the Haber process

Answer 2

1. Reactants are obtained (hydrogen from natural gas, nitrogen from air).
2. The gases are compressed to 200 atm and heated to 450oC before
   being pumped into a tank containing layers of catalytic iron beads.
3. Ammonia forms.
4. Ammonia and unreacted hydrogen and nitrogen pass into a cooling
   tank where the ammonia is collected as a liquid.
5. The unreacted hydrogen and nitrogen are recycled back into the tank.

Question 3

What is meant by the term dynamic equilibrium?

Answer 3

The rate of the forward reaction equals the
rate of the backwards reaction. The
concentration of reactants and products are
constant.

Question 4

What is the chemical equation for the formation of

ammonia from hydrogen and nitrogen?

Answer 4

N2 + 3H2 ⇌ 2NH3

Check google if unsure

Question 5

What are the ideal conditions for the Haber process?

Answer 5

• 450°C temperature
• 200 atm pressure
• Iron catalyst

Question 6

How is the rate of attainment of equilibrium affected

by temperature?

Answer 6

A higher temperature means equilibrium is
reached quicker. This is because the reacting
particles have more kinetic energy so there
are more frequent successful collisions.

Question 7

How is the rate of attainment of equilibrium affected

by a catalyst?

Answer 7

Equilibrium is reached faster when a
catalyst is used because the catalyst
provides an alternative reaction pathway
with a lower activation energy.

Question 8

How is the rate of attainment of equilibrium affected

by pressure?

Answer 8

Equilibrium is reached faster with a higher
pressure. This is because there are more particles
in the same volume (or the same number of
particles in a smaller volume) so more collisions
between reacting particles.

Question 9

How is the rate of attainment of equilibrium affected

by concentration?

Answer 9

Equilibrium is reached faster at a higher
concentration. This is because there are
more particles in the same volume so more
collisions between the reacting particles.

Question 10

Why are the conditions used in the Haber process a

compromise?

Answer 10

• A high temperature increases the rate of reaction however, it will
  favour the reverse reaction, decreasing the yield. Acompromise of
  450oC is used to obtain a sufficient rate and yield.
• A high pressure speeds up the rate and favours the forward
  reaction (increasing the yield). High pressures can be dangerous
  and require expensive machinery so a compromise of 200 atm is
  used.

Question 11

Why is a catalyst used in the Haber process?

Answer 11

To increase the rate of reaction so more
product is produced within the same
time frame.

Question 12

What factors should be considered before deciding the conditions for an industrial reaction?

Answer 12

• Availability and cost of raw materials.
• Energy requirements.
• Optimum temperature and pressure for high yield and fast rate of reaction.
• Need for a catalyst

Question 13

What is the purpose of fertilisers?

Answer 13

To promote plant growth

Question 14

What chemical compounds might fertilisers contain?

Answer 14

Nitrogen, phosphorus and potassium

compounds.

Question 15

What compounds are found in NPK fertilisers?

Answer 15

A combination of all three fertiliser
compounds: nitrogen, phosphorus and
potassium compounds

Question 16

Which parts of plant growth do the compounds

nitrogen, potassium and phosphorus help with?

Answer 16

Nitrogen: Healthy leaves.
Phosphorus: Healthy roots.
Potassium: Growth and healthy fruit /
flowers.

Question 17

Which ammonium salt is most commonly used in

fertilisers?

Answer 17

Ammonium nitrate

Question 18

How is the salt ammonium nitrate formed? Write a

chemical equation for the reaction taking place

Answer 18

React ammonia with nitric acid

NH3 + HNO3 → NH4NO3

(Check google if unsure)

Question 19

What is the chemical equation for the formation of

ammonium sulfate from ammonia and sulfuric acid?

Answer 19

2NH3 + H2SO4 → (NH4)2SO4

Check google if unsure

Question 20

How can ammonium sulfate be prepared in a laboratory?

Answer 20

Titration between ammonia and sulfuric acid:

• Exact volume of NH3 added to a conical flask using a pipette.
• Add a few drops of indicator.
• Add H2SO4 from the burette drop by drop. Stop when the indicator changes
  colour.
• Repeat, adding the exact volumes of reactants without the indicator (as it is
  an impurity).
• Remove the water by evaporation and crystallisation, leaving pure crystals.

Question 21

How can ammonium sulfate be produced on an

industrial scale?

Answer 21

Raw materials obtained from the Haber process (ammonia) and the contact process (sulfuric acid).

A large reactor chamber is filled with ammonia gas.

Sulfuric acid is sprayed into the chamber from above.

Ammonium sulfate crystals are produced.

Question 22

Compare the laboratory method of producing ammonium sulfate with the industrial process

Answer 22

Laboratory method:

• Faster rate of reaction.
• Small reactant quantities can easily be
  bought.
• Room temperature and pressure
• Simple equipment required.
• Very small yield.

Industrial process:

• Very expensive and complex.
• Continuous process so continuous yield.
• Large volumes of product.
• Slow rate of reaction.
• High energy requirement.
• Other industrial processes required to obtain the reactants.