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Chemistry > 12 - Alkanes > Flashcards

12 - Alkanes Flashcards

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1
Q

What are alkanes?

A

Saturated hydrocarbons
General formula - CnH2n+2

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2
Q

What are the physical properties of alkanes?

IMF

A

Relatively non-polar as main IMF’s are van der Waal’s.

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3
Q

What are the chemical properties of alkanes?

Reactivity, Combustion, Reacts

A

Relatively unreactive
Don’t react with acids, bases or oxidising/reducing agents
Can combust
Reacts with halogens.

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4
Q

What is crude oil?

A

A mixture of branched and unbranched alkanes.

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5
Q

What is a fraction?

A

A simplified mixture of hydrocarbons with similar boiling points, due to similar sized carbon chains.

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6
Q

What is fractional distillation?

A

The separation of a mixture into fractions by vaporising the mixture. The vapour is passed through columns with the temperature decreasing slowly. Based on the alkanes boiling point they condense at the different temperatures, separating the mixture.

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7
Q

What are the uses of gases from fractional distillation?

A

Fuel

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8
Q

What are the uses of petrol from fractional distillation?

A

Car fuel

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9
Q

What are the uses of kerosene from fractional distillation?

A

Jet fuel

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10
Q

What are the uses of diesel from fractional distillation?

A

Lorry fuel

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11
Q

What are the uses of lubricating oil from fractional distillation?

A

Engines

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12
Q

What are the uses of fuel oil from fractional distillation?

A

Ships

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13
Q

What are the uses of bitumen from fractional distillation?

A

Roofing

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14
Q

What is cracking?

A

Breaking large chain molecules into smaller more volatile and useful alkanes and alkenes.

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15
Q

What are the conditions for thermal cracking?

A

High temperature (1000K)
High pressure (7000kPa)
Kept in conditions for 1 second to avoid full decomposition.

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16
Q

What happens to the alkane during cracking?

A

The C-C breaks and each carbon gets 1 shared electron. They form highly reactive free radicals which react to form a variety of shorter chain molecules.

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17
Q

What does a catalyst do?

A

Provides an alternative pathway with lower activation energy.

18
Q

What is a zeolite?

A

A honeycomb structure with an enormous surface area.

19
Q

What are the conditions of catalytic cracking?

A

Lower temperature at 720K
Lower pressure (still greater than normal)
Uses a zeolite catalyst consisting of silicon dioxide and aluminium oxide.

20
Q

Compare the products of thermal vs catalytic cracking.

A

Thermal - high proportion of alkenes.
Catalytic - branched alkanes, cycloalkanes, aromatic compounds.

21
Q

What is the test for alkenes?

A

Turns bromine water colourless.

22
Q

Why is cracking important?

A

To reach the high demand for shorter chain alkanes, as they are more reactive and better fuels.

23
Q

What does complete combustion produce?

A

Carbon dioxide
Water

24
Q

What are the conditions for complete combustion?

A

Excess/ plentiful supply of oxygen.

25
Q

What are the products of incomplete combustion?

A

Carbon monoxide
Water
Soot (unburnt carbon)

26
Q

What are the conditions for incomplete combustion?

A

Limited supply of oxygen.

27
Q

How do sulphur impurities negatively affect the environment?

A

When the fuel is burnt the sulphur reacts with oxygen to form sulphur dioxide.
The sulphur dioxide is further oxidised to produce sulphur trioxide. This reacts with water to form sulphuric acid, which falls as acid rain, damaging wildlife and corroding buildings.

28
Q

What is the risk of carbon monoxide?

A

It is toxic as it binds to haemoglobin reducing its ability to carry oxygen, suffocating you.

28
Q

What are the risks of soot/ carbon particles?

A

Causes breathing problems, such as asthma.
Can block ventilation, leading to a carbon monoxide build up.

29
Q

How are nitrogen oxides formed?

A

Nitrogen from the atmosphere gets into the internal combustion engines, which at high temperatures reacts with oxygen to form nitrogen oxides.

30
Q

How do nitrogen oxides affect the environment?

A

They react with water vapour to form nitric acid, which falls as acid rain, damaging wildlife and corroding buildings.

31
Q

What is photochemical smog and its impacts?

A

Unburnt hydrocarbon and nitrogen oxides.
Causes respiratory problems and damages vegetation.

32
Q

What are greenhouse gases?

And examples

A

Gases that absorb long wave electromagnetic radiation (infrared) and re-emits them.
Carbon dioxide, water, methane.

33
Q

What are the effects of greenhouse gases?

A

They trap heat and raise the temperature of the planet, this causes global warming, causing sea levels to rise, destroying ecosystem and intense weather conditions.

34
Q

What are carbon neutral activities?

A

Activities that produce no carbon dioxide emissions overall.

35
Q

What is flu gas desulphurization?

A

The process of removing sulphur dioxide from flue gases emitted by burning fossil fuels.

36
Q

What is the process of flu gas desulphurization?

A

By reacting the gases with calcium carbonate (limestone) or calcium oxide (lime), to form gypsom which can be used for plaster or plasterboard.

37
Q

What is a catalytic converter?

What does it remove and produce

A

A device that produces less harmful products form an internal combustion engine by catalyzing a redox reaction. It removes unburnt hydrocarbons, carbon monoxide and nitrogen oxide, forming nitrogen, carbon dioxide and water.

38
Q

What effect does increasing the carbon chain have on the melting/ boiling point?

A

Increase
The longer the carbon chain the stronger the van der Waal’s forces, therefore more energy is required to overcome the forces.

39
Q

What effect does branching have on the melting/ boiling point?

A

Decrease
As the surface area of the molecule decreases the van der Waal’s forces get weaker, therefore it requires less energy to overcome the forces.

Chemistry (17 decks)

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