2 - Combustion of alkanes

Question 1

Why are alkanes used as fuels?

Answer 1

They readily burn in the presence of oxygen and release heat energy when burnt

Question 2

In excess oxygen alkanes will undergo…

Answer 2

complete combustion

Question 3

What are the products of complete combustion?

Answer 3

• CO_{2 (g)}
• H₂O _(l)

Question 4

In limited amounts of oxygen alkanes will undergo…

Answer 4

incomplete combustion

Question 5

What are the products of incomplete combustion?

Answer 5

• CO _(g) OR C _(s)
• H₂O _(l)

Question 6

What pollutants are produced by internal combustion engines?

Answer 6

• Nitrogen oxides
• Carbon monoxide
• Carbon
• Unburned hydrocarbons

Question 7

What is the environmental consequence of nitrogen oxides?

Answer 7

• NO is toxic and can form acidic gas NO₂
• NO_{2 is toxic and acidic and forms acid rain}

Question 8

What is the environmental consequences of carbon monoxide?

Answer 8

Carbon monoxide is a toxic gas that binds to haemoglobin, preventing the binding of oxygen

Question 9

What is the environmental consequence of carbon dioxide?

Answer 9

Contributes to global warming

Question 10

What is the environmental consequence of unburnt hydrocarbons?

Answer 10

Contributes towards to formation of smog

Question 11

What is the environmental consequence of soot (C)?

Answer 11

Global dimming and respiratory problems

Question 12

What do catalytic converters do?

Answer 12

They remove CO, NO_x and unburned hydrocarbons from exhaust gases by turning them into ‘harmless’ CO₂, N₂ and H₂O

Question 13

Write the equation of when carbon monoxide and nitrogen oxide react together in a catalytic converter

Answer 13

2CO + 2NO → 2CO₂ + N₂

Question 14

Catalytic converters have a ceramic honeycomb coated with a thin layer of catalyst metals. Why is a thin layer used?

Answer 14

• To reduce the amount of metals needed
• Allows for a larger surface area

Question 15

What are the 3 metal catalysts used in a catalytic converter?

Answer 15

• Platinum
• Palladium
• Rhodium

Question 16

Combustions of hydrocarbons containing sulfur leads to the production of…

Answer 16

sulfur dioxide

Question 17

How can sulfur dioxide cause air pollution?

Answer 17

Sulfur dioxide will dissolve in atmospheric water and can produce acid rain

Question 18

Gases given out by power stations are called flue gases which contain sulfur dioxide. How can this be removed?

Answer 18

Through a process called flue gas desulfurisation
- A slurry of either calcium oxide or calcium carbonate with water is sprayed into the flue gases
- Flue gas reacts with the slurry and forms calcium sulfite
- This can be further oxidised to calcium sulfate