2.6 - Reversible reactions, industrial processes, and important chemicals Flashcards
What is a reversible reaction?
A reaction which occurs in 2 directions
The products can react to form the original reactants
A+B ⇌ C+ D
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
Same
How can the direction of a reversible reaction be changed?
By changing the conditions:
Pressure
Temperature
Concentration of reactants or products
If the forward reaction is exothermic, will the backward reaction be endothermic or exothermic?
Endothermic, the same amount of energy is released
What can ammonia be used for?
To produce nitrogen-based fertilisers
How can the presence of ammonia gas be tested?
Damp red litmus paper will turn blue as ammonia is alkaline
How can the presence of ammonium ions be tested? What is the ionic equation for this?
1) Add solution containing hydroxide ions
2) Test for ammonia gas
NH4+(aq) + OH–(aq) → NH3(g) + H2O(l)
Where can nitrogen and hydrogen gas be obtained from?
Nitrogen: from air
Hydrogen gas: reacting natural gas with steam or other sources
What are the conditions required for the Haber process?
High temperature - 350°C to 450°C
a high pressure – 150 to 200 atmospheres
an iron catalyst
What happens during the Haber process?
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
What is the reaction in the Haber process?
Nitrogen + Hydrogen = Ammonia
N2 + 3H2 ⇌ 2NH3
What are the disadvantages of using a low temperature and very high pressure?
Low temp: Slower rate of reaction
High pressure: Requires high energy
What are the two things aimed to be maximized when choosing the conditions of the Haber process
Rate of reaction and yield of ammonia
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.
increases
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.
decreases
After a while what happens to the iron catalyst in the Haber process? And what is needed to be done?
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.
What are the advantages of fertilisers?
Increase crop yield and growth
Increases profit for farmers
What are the disadvantages of fertilisers?
Eutrophication- when fertilisers are washed off into rivers and lakes (algae grows, block sunlight, Bacteria Oxygen)
Turns soil acidic
Can cause baby blue syndrome
What kinds of reactions are used to make nitrogenous fertilisers from ammonia?
Neutralisation reactions
What are some examples of nitrogenous fertilsers?
Ammonium sulfate
Ammonium nitrate
What raw materials are needed to make sulfuric acid?
Sulfur
Air
Water
What does it mean for Sulfuric acid to be a strong acid
It completely dissociates in water to release H+ ions
What is the molecular formula of sulfuric acid?
H2SO4
What is the contact process?
The manufacture of sulfuric acid
What is the first step of the Contact process?
Sulfur is burned in air and reacts with oxygen to form sulfur dioxide
S(l) + O2(g) → SO2(g)
What is the second stage of the Contact process?
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)
What is the third (final) step of the Contact process?
Sulfur trioxide reacts with water to form sulfuric acid
H2O(l) + SO3(g) → H2SO4(aq)
Which is the reversible step in the Contact process and what are the conditions for this reaction?
The 2nd step: 2SO2(g) + O2(g) ⇌ 2SO3(g)
Catalyst: Vanadium (V) oxide (V2O5)
Temp: 450°C
Pressure: 2atm
What are the uses of sulfuric acid?
1) Mostly used to make fertilisers
2) Manufacture of chemicals (detergents, paints, dyes, artificial fibres)
3) processing metals
4) manufacture of rayon
What does a dehydrating agent do?
Removes water from other compounds
How does concentrated sulfuric acid act as a dehydrating agent with sugar?
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
What change can be observed when concentrated sulfuric acid act as a dehydrating agent on hydrated copper (II) sulfate?
Blue crystals (hydrated copper sulfate) –> white powder (anhydrous copper sulfate)
