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Organic Chemistry > 3.3.2.3 Combustion of Alkanes > Flashcards

3.3.2.3 Combustion of Alkanes Flashcards

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1
Q

Why is the the combustion of alkanes important?

A

Alkanes are used as fuels

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2
Q

What is the complete combustion of an alkane?

A

When an alkane is burnt with oxygen in excess

So that the product is carbon dioxide and water

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3
Q

What is the incomplete combustion of an alkane?

A

The alkane doesn’t burn in an oxygen supply plentiful enough so the products formed are (along with water)
Carbon monoxide
Or
Soot

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4
Q

Is combustion exo or endo thermic?

A

Exothermic

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5
Q

What are soot and carbon monoxide considered to be?

A

Pollutants

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6
Q

What is the chemical formula of Carbon Monoxide and what is it’s state symbol?

A

CO (g)

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7
Q

What makes CO(g) dangerous?

A

It is a colourless, odourless toxic gas making it hard to detect
It binds irreversibly to haemoglobin
Results in suffocation

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8
Q

How is soot dangerous to people’s health?

A

Passes deep into lungs and cannot be removed

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9
Q

Why is soot bad for engine parts?

A

Reduces power of engine
Less energy given out by fuel
More fuel needs to be burnt to output same amount of energy

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10
Q

Why is soot bad for the environment?

A

Contributes to global dimming

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11
Q

What are greenhouse gases?

A

Gases in the atmosphere which can absorb and emit infra red radiation thus warming the atmosphere. They are not inherently bad and they are why the earth has a temperature which can sustain life

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12
Q

Give 5 examples of greenhouse gases

A
  1. Carbon dioxide
  2. Hydrocarbons
  3. Water vapour
  4. Methane
  5. Nitrous oxide (N2O)
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13
Q

Name 3 other main pollutants

A
  1. Unburnt hydrocarbons
  2. Sulphur dioxide
  3. Nitrogen oxides
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14
Q

How do unburnt hydrocarbons end up in the atmosphere?

A

Pass through engines unburnt

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15
Q

Why are unburnt hydrocarbons bad?

A

They waste fuel
They’re air pollutants
They’re carcinogenic
They’re greenhouse gases

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16
Q

How is the formation of unburnt hydrocarbons prevented?

A

Careful mixing of air with fuel reduces unburnt hydrocarbons

Can be removed in catalytic converters

17
Q

How does the pollutant sulphur dioxide arise?

A

Fuels that contain sulphur undergo combustion

18
Q

Write the equation for the combustion of sulphur

A

S + O2 => SO2

19
Q

Why is sulphur dioxide bad for the environment?

A

As an acidic dioxide, it reacts with water to form acid rain. This damages limestone buildings and kills marine life

20
Q

Why is sulphur dioxide harmful to health?

A

Causes respiratory problems

21
Q

How is the formation of sulphur dioxide prevented?

A

Removed from fuel before burning

Or SO2 removed from fumed post combustion

22
Q

What is the name of the mechanical process that removes

SO2 from fumes?

A

Flue gas desulphurisation

23
Q

Describe the process of flue has desulphurisation

A
  1. Waste gases pass through scrubber, I.e. calcium oxide/calcium carbonate
  2. An acid-base reaction takes place
  3. Product of gypsum, CaSO3 which is used to make plasterboard
24
Q

What causes the formation of nitrogen oxides?

A

Sparks and very high temperatures in engines cause N2 to react with O2 forming either NO or NO2, collectively referred to as NOx

25
Q

Why is NOx dangerous for the environment?

A

Reacts with water and oxygen to form acid rain

26
Q

How is the amount of NOx and CO and unburnt hydrocarbons produced in cars controlled

A

Use of catalytic converters

27
Q

What do catalytic converters do?

A

Remove CO, NOx and unburned hydrocarbons from exhaust gases and turn them into CO2, N2 and H2O

28
Q

Write the equations for the conversion undertaken by a catalytic converter

A

2CO + 2NO => 2CO2 + N2
2NO => N2 + O2
C3H8 (unburnt alkane) + 5O2 => 3CO2 + 4H2O

29
Q

What coats the ceramic honeycomb in a catalytic converter?

A

Catalyst metals e.g. Pt, Pd and Rh

30
Q

Why do catalyst metals coat the ceramic honeycombs?

A

Less expensive

Provide large surface area

31
Q

Give at least one example of a precious metal used in a catalytic converter

A

Platinum

32
Q

Write an equation for desulphurisation by calcium oxide

A

CaO + SO2 => CaSO3

Organic Chemistry (6 decks)

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