Unit 2.6 Reversible Reactions, Industrial Processes and Important Chemicals

What is a reversible reaction

A reaction which occurs in 2 direction, the product can react to form the original reactants.

A+B⇌C+D

For A+B⇌C+D, which are the products for the forward reaction and which are the product for the backward reaction?

1. Forward = C+D

2. Backward = A+B

How can the direction of a reversible reaction be changed

Changing these condition

• Pressure

• Temperature

• Concentration

If the forward reaction is exothermic, will the backward reaction be endothermic or exothermic

Endothermic, the same amounts of energy is transferred

What is the reaction in Haber process

Nitrogen + Hydrogen ⇌ Ammonia

N2 + 3H2 ⇌ 2NH3

What can ammonia be used for

To produce nitrogen-based fertiliser

Where can nitrogen and hydrogen gas be obtained

Nitrogen = air

Hydrogen - natural gas or other sources

What condition required for the Haber Process

High temperature (450 degree)

High pressure (200 atm)

Iron catalyst

What happens during the Haber Process

1. Purified bases passed over iron catalyst

2. Some nitrogen and hydrogen reacts to form ammonia

3. Some ammonia breaks down into nitrogen and hydrogen because the reaction is reversible

4. Mixture is cooled, ammonia liquefies and is removed

5. Remaining nitrogen and hydrogen is recycled

What does it mean for the Haber proceed to be in dynamic equilibrium

Forward and backward reaction happen at a constant rate once equilibrium is reached

In which way does the equilibrium shift in the Haber process when pressure is increased? Why?

Equilibrium shift to the right. Because the total number of mole of gas is fewer on the right

The forward reaction of the Haber process is exothermic. How can the conditions be changed to produce more ammonia?

By lowering the temperature, the forward reaction is favoured

What are the disadvantage of using a low temperature and very high pressure

Low temperature = slow rate of reaction

High pressure = requires high energy

What are the two things aimed to be maximised when choosing the condition of the Haber process

Rate of reaction and the yield of ammonia

How can the presence of ammonia gas be tested

Moist red litmus paper will grin blue as ammonia is alkaline

How can the presence of ammonium ions be tested? What is the ionic equation for this reaction

1. Add solution containing hydroxide ion such as NaOH

2. Test for ammonia gas

NH4 + OH —> NH3 + H20

What kind of reactions are used to make nitrogenous fertiliser from ammonia

Neutralisation reaction

What are some example of nitrogen Ouse fertiliser

• Ammonium sulfate

• Ammonium nitrate

How can ammonium sulfate be formed from sulfuric acid

Ammonia + Sulfuric acid —> Ammonium sulfate

Ammonium hydroxide + sulfuric acid —> ammonium sulfate + water

What are the 2 ways used to form ammonium nitrate from nitric acid

Ammonia + nitric acid —> ammonium nitrate

Ammonium hydroxide + nitric acid —> ammonium nitrate + water

What are the advantage of using fertiliser

Increases crop yield and growth

Increase profit for farmer

What are the disadvantage of using fertiliser

• Eutrophication when fertiliser are washed off into rivers and lakes

• Change pH of soil

• Cause cause baby blue syndrome

What does it mean for sulfuric acid to be a strong acid

It completely dissociated H+ ion in aqueous solution

What is the molecular formula and structure of sulfuric acid

H2SO4

What is the contact process

The manufacture of sulfuric acid

What is the first, second and final step of the contact process

1. Sulfur is burned in air and reacts with oxygen to form sulfur dioxide

   S + O2 —> SO2

2. Sulfur dioxide reacts further with oxygen to form Sulfur trioxide

   2SO2 + O2 ⇌ SO3

   • Reversible

   • Temperature = 450

   • Catalyst = V2O5

   • Pressure = 2atm

3. Sulfur trioxide reacts with water to form sulfuric acid

   H2O + SO3 —> H2SO4

What are the uses of sulfuric acid

• Fertiliser

• Processing metals

• Petroleum refining

What does a dehydrating agent do

Removes water from other compounds

How does concentrated sulfuric acid acts as a dehydrating agent with sugar

• Concentrated sulfuric acid removes 6 water molecule per glucose molecule

• Highly exothermic reaction

• Water molecules released as steam and a black mass of carbon forms

What change can be observed when concentrated sulfuric acid act as a dehydrating agent on hydrated copper sulfate

Blue crystal (hydrated cooper sulfate) —> white powder (anhydrous copper sulfate)