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AS Chemistry > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What are alkanes?

A

A homologous series of saturated hydrocarbons

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2
Q

What are hydrocarbons?

A

Compounds which only contain hydrogen and carbon

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3
Q

What is a saturated hydrocarbon?

A

A hydrocarbon which only contains single bonds, no double bonds

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4
Q

How is methane produced?

A

Anaerobic respiration in cows and sheep, compost heaps, rice fields and landfill waste tips

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5
Q

Why are alkanes non-polar?

A

Because there’s a small difference in electronegativity between the carbon and the hydrogen

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6
Q

What intermolecular forces exist between alkane molecules?

A

Van der Waals forces

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7
Q

How does the Mr of compounds affect the strength of the intermolecular forces?

A

Greater Mr = stronger forces

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8
Q

Why do branches chained isomers have a lower melting and boiling point?

A

Smaller surface area in contact with each other and do not fit together as closely

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9
Q

What substances can you dissolve alkanes in?

A

Non-polar liquids like hexane and cyclopetane

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10
Q

How can you separate mixtures of alkanes?

A

Fractional distillation

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11
Q

What is crude oil?

A

A mixture containing mainly alkane hydrocarbons that can be separated by fractional distillation

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12
Q

How is crude oil made?

A

Remains of animals and plants get covered in mud at the bottom of the ocean and the high pressure and temp change the mud so the animal and plant remains turn into crude oil

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13
Q

What is fractional distillation?

A

The continual evaporation and condensation of a mixture causing it to separate into its components due to a difference in their boiling points

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14
Q

What is a fraction?

A

Group of compounds with similar boiling points and are removed at the same level of a fractionating column

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15
Q

Explain how fractional distillation works

A

Crude oil heated in a furnace until part of it turns into a vapour. Vapour rises up a fractionating column where it’s cooler as you go up and it condenses at its boiling point and it’s piped off

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16
Q

Where are short chain molecules collected in a fractionating column?

A

At the top bc its cooler there and they have a lower boiling point

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17
Q

What is cracking?

A

The process where long chain hydrocarbon molecules are broken into shorter chain molecules which are high in demand bc they’re more useful

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18
Q

Describe the conditions of thermal cracking

A

High temp of 1000-1200K and high pressure of 70atm for 1s

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19
Q

What is produced when long chain alkanes are cracked thermally?

A

Short chain alkanes and alkenes

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20
Q

Why are the conditions in thermal cracking applied for a short amount of time?

A

Because the high temp and pressure could decompose the alkanes into carbon and hydrogen

21
Q

Describe the conditions needed in catalytic cracking

A

Temp of 800-1000K, pressure of 1-2atm and a zeolite catalyst

22
Q

What is a zeolite catalyst?

A

Acidic mineral with a honeycomb structure made from aluminium oxide and silicon dioxide

23
Q

Why is zeolite’s honeycomb structure good?

A

Large surface area which increases the rate of reaction

24
Q

Why are high temperatures needed in cracking?

A

To break the strong carbon-carbon bonds in the alkanes which require a lot of energy to overcome

25
Q

What do alkanes that burn in oxygen produce?

A

Carbon dioxide and water

26
Q

What do alkanes that burn in a limited supply of oxygen produce?

A

Water and carbon monoxide

27
Q

Why is carbon monoxide dangerous?

A

Reacts with haemoglobin in the blood and prevents them from carrying oxygen to all of the cells in the body

28
Q

What does catalytic cracking produce?

A

motor fuels and aromatic hydrocarbons

29
Q

What pollutants do internal combustion engines form?

A

nitrogen oxides, carbon monoxide, carbon particles, sulfur dioxide and unburnt hydrocarbons

30
Q

Why are nitrogen oxides formed in an internal combustion engine?

A

Bc of the high tempeerature and pressure

31
Q

Why is sulfur dioxide formed in an internal combustion engine?

A

Because there may be sulfur in the impurities of the crude oil

32
Q

What is the greenhouse effect?

A

The effect of trapping the energy from the sun

33
Q

What is global warming?

A

The increasing average temperature of the atmosphere at the surface of the Earth

34
Q

Name three greenhouse gases

A

Water vapour, methane and carbon dioxide

35
Q

What is the origin of water vapour?

A

Occurs naturally in the atmosphere

36
Q

What is the origin of carbon dioxide?

A

Produced in respiration and combustion

37
Q

What is the origin of methane?

A

Product of digestion from cows and sheep

38
Q

What causes global warming?

A

Changing the balance of the concentration of greenhouse gases bc they trap more heat from the sun so the Earth’s temperature increases

39
Q

Why is rain water a weak acid?

A

Bc of naturally occuring Co2 in the atmosphere

40
Q

What causes acid rain?

A

Sulfur dioxide from the impurities of fossil fuels dissolving in rain water then being oxidised to form sulfuric acid

41
Q

Why is acid rain harmful?

A

Bc it destroys trees and vegetation, corrodes buildings, kills fish and also can fall far from the source

42
Q

What causes photochemical smog?

A

Gases like nitrogen oxides, sulfur dioxide and unburnt carbon fuels react with sunlight and carbon atoms from incomplete combustion

43
Q

How do catalytic converters reduce greenhouse gas emissions?

A

Converting harmful gases into less harmful gases using a catalyst

44
Q

What catalysts are used in a catalytic converter?

A

Rhodium and platinum

45
Q

Why is a thin layer of metal catalyst used in a catalytic converter?

A

Large surface area increases the rate of conversion and also small amount of expensive metal is used

46
Q

How is the amount of sulfur dioxide released into the atmosphere reduced?

A

Flue gas desulfurisation

47
Q

Explain the process of flue gas desulfurisation

A

Gases passed through a slurry of calcium oxide which neutralises the acid bc it’s a base and forms calcium sulphite

48
Q

What is done with the products of the flue gas desulfurisation?

A

Calcium sulphite is oxidised to calcium sulfate to be used as a construction material

AS Chemistry (14 decks)

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