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Chemistry > Fuels And Heats Of Reaction > Flashcards

Fuels And Heats Of Reaction Flashcards

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1
Q

What are hydrocarbons?

A

Compounds consisting of hydrogen and carbon only, bonded together covalently

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2
Q

Give an example of a hydrocarbon

A

CH4 - Methane

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3
Q

What are the importance of hydrocarbons

A

Fuels for combustion

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4
Q

Sources of hydrocarbons

A

Fossil fuels, crude oil, natural gas and coal

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5
Q

Fossil fuels formed?

A

Remains of dead animals and plants

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6
Q

Crude oil and natural gas formed?

A

Remains of marine animals and plants

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7
Q

Methane formed

A

Digestive tracts [cattle] - greenhouse effect

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8
Q

What are aliphatic hydrocarbons?

A

Straight and branched chains or rings of carbon atoms other than benzene ring

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9
Q

Aromatic hydrocarbons

A

Benzene-type ring

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10
Q

What is a homologous series?

A

It’s a family of organic compounds with the same general formula, similar chemical properties and successive members differing by CH2

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11
Q

General formula for alkanes

A

CnH2n + 2

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12
Q

What kinda bonds to alkanes have

A

Single bonds = saturated

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13
Q

Physical properties of alkanes

A

Non- polar = insoluble in water but soluble in cyclohexane

Low boiling points = van der waal’s forces are easy to break

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14
Q

What are isomers?

A

Compounds that have the same molecular formula but a different structural formula

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15
Q

What kind of bonds to alkenes have?

A

Double bond = unsaturated

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16
Q

What’s the general formula for alkenes?

A

CnH2n

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17
Q

Physical properties of alkenes

A

Non polar

Low boiling point - the longer the chains the stronger the forces - higher boiling point

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18
Q

What kind of bond in alkynes?

A

Triple bonds = unsaturated

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19
Q

Physical properties of alkynes?

A

Low or zero polarity

Low boiling points

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20
Q

What is dehydrocyclisation?

A

Involves converting chains into rings by removing 2H by heating in presence of suitable catalyst

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21
Q

What is catalytic cracking?

A

Breaking long chains into shorter chains by heating in the absence of oxygen and presence of a catalyst
[some saturated some unsaturated]

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22
Q

The products of catalytic cracking what are they used for?

A

Unsaturated - used as feedstock for polymer industry

Saturated - high octane, used for making petrol

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23
Q

Advantages of catalytic cracking

A

Long chain compounds - converted into more useful compounds

Saturated and unsaturated

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24
Q

Purpose of dehydrocyclisation in oil refining?

A

Increases octane number which reduces tendency of fuel to cause knocking

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25
Q

What is hess’s law?

A

Heat change of a reaction depends on the initial and final states or the reaction and is indecent of the route taken

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26
Q

What is the name of the oil refining process?

A

Fractional distillation

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27
Q

Identify the physical property that is the basis for hydrocarbons in oil refining being isolated as naphtha?

A

Boiling point

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28
Q

What is oil refining?

A

When compounds in crude oil are separated according to different boiling points

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29
Q

Give a major use for kerosene

A

Jet fuel

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30
Q

Give a make use for residue

A

Road making

31
Q

Why are isomerisation and catalytic cracking desirable?

A

Increase octane number which reduces tendency of fuel to cause knocking

32
Q

Identify a property of a hydrocarbon that results in its presence in a particular fraction in oil refining

A

Boiling point

33
Q

Name the fraction in oil refining that is used for jet fuel

A

Kerosene

34
Q

What process is used to convert molecules in the fraction to smaller molecules that are in greater demand

A

Catalytic cracking

35
Q

What are the two reference hydrocarbons used to assign octane numbers to fuels?

A

Heptane and 2,2,4 tri-methylpentane

36
Q

Give two advantages of adding oxygenates?

A

Increases octane number which reduces knocking

And reduces pollution

37
Q

Give an example of an oxygenate

A

MTBE

Methyl tertiary- butyl ether

38
Q

Give two properties of hydrogen that makes it a fuel choice?

A

Low density

High octane number

39
Q

State one disadvantage of hydrogen as a fuel

A

Explosive

40
Q

Give two ways hydrogen gas is produced industrially

A

Electrolysis of water

Steam reforming of natural gases [ch4]

41
Q

Name two structural feature of hydrocarbons with high octane numbers

A

Short chains, branches

42
Q

What is the octane number?

A

Measure of the tendency of a fuel to cause knocking

43
Q

How can members of same homologous group differ in boiling point?

A

Smaller - fewer electrons and lower mr

Therefore weaker intermolecular forces

44
Q

Define heat of combustion

A

Heat change when one mole of a substance is burned completely in excess oxygen

45
Q

State the octane number of 2,2,4 trimethylpentane

A

100

46
Q

Explain why MTBE is sometimes added to fuel

A

Increases octane number and reduces pollution

47
Q

Name the substance previously added to motor fuel and why was it stopped

A

Tetraethyl lead - toxic [harmful for the environment] and also poisonous to catalytic converters

48
Q

What lab apparatuses is used to measure heats of combustion?

A

Bomb calorimeter

49
Q

Explain the term isomerisation

A

In presence of heat and suitable catalyst where structural formula is changed and hydrocarbons become branched

50
Q

How do you know one hydrocarbon has a higher octane number than the other?

A

Shorter chain and more branches = higher

51
Q

What is the nature of the chemicals that make up the bulk of crude oil?

A

Hydrocarbons

52
Q

Describe how crude oil is separated into useful substances in an oil refinery

A

Hot crude oil enters the base of column and is heated at the bottom
Vapour moves up series of trays
Depending on b.p
High b.p - fractions come off at lower levels
Low b.p - fractions come off at higher levels

53
Q

Major use for light gasoline and naphtha fractions of crude oil?

A

Petrol

54
Q

Why is catalytic cracking carried out in oil refining?

A

To give products with higher octane numbers

55
Q

Compounds Heptane and Methylbenzene are in the same fraction - which one? In oil refining

A

Naphtha

56
Q

Name two properties of compounds are responsible for compounds being found in same fraction in oil refining

A

Sim boiling point

Sim molecular mass

57
Q

What is auto ignition?

A

Ignition before spark is produced

58
Q

Name the three processes that are carried out in an oil refinery to modify the hydrocarbon structure and improve their octane number

A

1-isomerisation
2-dehydrocyclisation
3-catalytic cracking

59
Q

What are the six fractions in crude oil?

A
  1. Refinery gas
  2. Light gasoline [petrol]
  3. Naptha
  4. Kerosene
  5. Gas oil
  6. Residue

[RED PONIES NEVER KICK GOOD RIDERS]

60
Q

Give a use of refinery gas

A

Domestic heating gas

61
Q

Give a use of light gasoline

A

Motor fuel

62
Q

Give a use of Naphtha

A

Solvents

63
Q

Give a use of kerosene

A

Aviation fuel

64
Q

Give a use for gas oil

A

Diesel

65
Q

Give a use for residue

A

Bitumen, lubricating oil

66
Q

How is hydrogen as a fuel produced and give an equation

A

Steam reforming of methane

CH4 + H20 = CO + 3H2

67
Q

Why are mercaptans added to natural gas?

A

For detection because they are odourless

68
Q

What are mercaptans

A

Sulfur compounds added to LPG and Natural has for detection because they are odourless

69
Q

What instrument is used to measure heat of combustion

A

Bomb calorimeter

70
Q

Two components liquified as LPG

A

Propane

Butane

71
Q

What is heat of reaction?

A

It’s the heat change in KJ/mol as a reaction proceeds according to a balanced chemical equation

72
Q

What is the principal use made of oxygenates such as MTBE in the petrochemicals industry?

A

Raise octane number which prevents auto-ignition

73
Q

Smoke Petrol Engine

A

Induction - Petrol vaporised + drawn with air into a cylinder as piston moves down
Compression - then compressed as piston moves back up and causes temp to rise
Ignition - petrol/air mixture is ignited by spark and resulting explosion pushes piston back down to supply energy to propel car
Exhaust - Waste are pushed out as piston rises back up cylinder

Chemistry (15 decks)

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