2.6 - Reversible reactions, industrial processes, and important chemicals

Question 1

What is a reversible reaction?

Answer 1

A reaction which occurs in 2 directions
The products can react to form the original reactants
A+B ⇌ C+ D

Question 2

In a reversible reaction - the amount of energy absorbed in the forward process is the same/different as the amount of energy released in the reverse process

Answer 2

Same

Question 3

How can the direction of a reversible reaction be changed?

Answer 3

By changing the conditions:
Pressure
Temperature
Concentration of reactants or products

Question 4

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

Answer 4

Endothermic, the same amount of energy is released

Question 5

What can ammonia be used for?

Answer 5

To produce nitrogen-based fertilisers

Question 6

How can the presence of ammonia gas be tested?

Answer 6

Damp red litmus paper will turn blue as ammonia is alkaline

Question 7

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

Answer 7

1) Add solution containing hydroxide ions
2) Test for ammonia gas

NH4+(aq) + OH–(aq) → NH3(g) + H2O(l)

Question 8

Where can nitrogen and hydrogen gas be obtained from?

Answer 8

Nitrogen: from air

Hydrogen gas: reacting natural gas with steam or other sources

Question 9

What are the conditions required for the Haber process?

Answer 9

High temperature - 350°C to 450°C
a high pressure – 150 to 200 atmospheres
an iron catalyst

Question 10

What happens during the Haber process?

Answer 10

1) Purified gases passed over iron catalyst
2) Some nitrogen and hydrogen reacts to form ammonia
3) Some ammonia breaks down into nitrogen and hydrogen (because reaction is reversible)
4) Mixture is cooled, ammonia liquefies and is removed
5) Remaining nitrogen and hydrogen recycled

Question 11

What is the reaction in the Haber process?

Answer 11

Nitrogen + Hydrogen = Ammonia

N2 + 3H2 ⇌ 2NH3

Question 12

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

Answer 12

Low temp: Slower rate of reaction

High pressure: Requires high energy

Question 13

What are the two things aimed to be maximized when choosing the conditions of the Haber process

Answer 13

Rate of reaction and yield of ammonia

Question 14

Increasing the pressure of the reaction _____ (increases/ decreases) the yield of ammonia. However, if the pressure is made too high, the equipment needed to safely contain the reaction becomes very expensive.

Answer 14

increases

Question 15

Increasing the temperature of the reaction actually ______ (increases/ decreases) the yield of ammonia in the reaction. This means that we could get a bigger yield of ammonia with a lower temperature. However, if the temperature is too low, the rate of the reaction would be so slow that it would take too long to make the ammonia.

Answer 15

decreases

Question 16

After a while what happens to the iron catalyst in the Haber process? And what is needed to be done?

Answer 16

The iron catalyst that is used to increase the rate of reaction will eventually stop working effectively. It is said that the catalyst is ‘poisoned’ and it will need to be replaced regularly.

Question 17

What are the advantages of fertilisers?

Answer 17

Increase crop yield and growth

Increases profit for farmers

Question 18

What are the disadvantages of fertilisers?

Answer 18

Eutrophication- when fertilisers are washed off into rivers and lakes (algae grows, block sunlight, Bacteria Oxygen)
Turns soil acidic
Can cause baby blue syndrome

Question 19

What kinds of reactions are used to make nitrogenous fertilisers from ammonia?

Answer 19

Neutralisation reactions

Question 20

What are some examples of nitrogenous fertilsers?

Answer 20

Ammonium sulfate

Ammonium nitrate

Question 21

What raw materials are needed to make sulfuric acid?

Answer 21

Sulfur
Air
Water

Question 22

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

Answer 22

It completely dissociates in water to release H+ ions

Question 23

What is the molecular formula of sulfuric acid?

Answer 23

H2SO4

Question 24

What is the contact process?

Answer 24

The manufacture of sulfuric acid

Question 25

What is the first step of the Contact process?

Answer 25

Sulfur is burned in air and reacts with oxygen to form sulfur dioxide
S(l) + O2(g) → SO2(g)

Question 26

What is the second stage of the Contact process?

Answer 26

Sulfur dioxide reacts further with oxygen to form sulfur trioxide

2SO2(g) + O2(g) ⇌ 2SO3(g)

Reversabile
Catalyst: vanadium (V) oxide (V2O5)
Temp : 450°C (chosen as a compromise temperature, giving a decent yield with a good rate of reaction)
Pressure: aprox 2 atm (the increased pressure favours the formation of SO3, but if the pressure is too high the risk of explosion is too great, given that SO3 is a highly acidic gas)

Question 27

What is the third (final) step of the Contact process?

Answer 27

Sulfur trioxide reacts with water to form sulfuric acid

H2O(l) + SO3(g) → H2SO4(aq)

Question 28

Which is the reversible step in the Contact process and what are the conditions for this reaction?

Answer 28

The 2nd step: 2SO2(g) + O2(g) ⇌ 2SO3(g)

Catalyst: Vanadium (V) oxide (V2O5)
Temp: 450°C
Pressure: 2atm

Question 29

What are the uses of sulfuric acid?

Answer 29

1) Mostly used to make fertilisers
2) Manufacture of chemicals (detergents, paints, dyes, artificial fibres)
3) processing metals
4) manufacture of rayon

Question 30

What does a dehydrating agent do?

Answer 30

Removes water from other compounds

Question 31

How does concentrated sulfuric acid act as a dehydrating agent with sugar?

Answer 31

Concentrated sulfuric acid removes 6 water molecules per glucose (C6 H12 O6) molecule.
Highly exothermic reaction
Water molecules released as steam and a black mass of carbon forms

Question 32

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

Answer 32

Blue crystals (hydrated copper sulfate) –> white powder (anhydrous copper sulfate)