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Chemistry 101 > Fuels & Thermochemistry > Flashcards

Fuels & Thermochemistry Flashcards

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1
Q

What are Mercaptans and why are they added to natural gas and LPG

A

They are sulphur compounds.

They are added to gas to give an odour so we can detect leaks

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2
Q

What are the 2 hydrocarbons used to assign octane numbers to fuels.

A

2,2,4-trimethylpentane and heptane

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3
Q

Define heat of Combustion

A

This is the heat change when one mole of the substance is completely burned in excess oxygen.

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4
Q

Define steam reforming

A

This is the reacting of methane with steam in the presence of a suitable catalyst.

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5
Q

What is the balanced equation for for steam reforming?

A

CH4 + H20 = 3H2 + CO2

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6
Q

Describe a method by which large quantities of hydrogen can be obtained from water.

A

Through the electrolysis of water using inert electrodes. Hydrogen is produced at the cathode.

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7
Q

State a disadvantage of using hydrogen as a fuel.

A

It is difficult to store.
It is difficult to transport
It is explosive

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8
Q

When Ethyne gas is produced, other than air name an impurity which could be found in the prepared sample

A

Ammonia
Hydrogen sulfide
Phosphine

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9
Q

Name the fraction obtained from crude oil that is used as fuel for jet aircraft.

A

Kerosene

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10
Q

Define octane number.

A

This is the measure of the tendency of the fuel to resist knocking.

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11
Q

State the 2 structural features of a hydrocarbon which contribute to having a high octane number.

A

A short chain
Highly branched
Cyclic structure.
Aromatic

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12
Q

Define homologous series

A

This is a series of compounds of similar chemical properties, showing gradations in physical properties, having a general formula for its members, each member having a similar method of preparation, each member differing from the previous member by a ch2 unit.

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13
Q

Give 2 named additives used to increase the octane number a fuel

A

methanol

ethanol

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14
Q

Name the separation technique used in an oil refinery to separate the fractions in crude oil.

A

Fractional distillation

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15
Q

Name a fraction with the carbon chain lengths to form petrol

A

Light gasoline

Naphtha

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16
Q

Name a fraction used to obtain bitumen

A

Residue

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17
Q

Write a balanced equation for the dehyldrocyclisation of hexane

A

C6H14 = C6H12 + H2

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18
Q

Name a process carried out in the oil refinery to modify hydrocarbon structures.

A

Catalytic Cracking

Isomerisation

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19
Q

What is the fractionation of crude oil

A

This is the separation of crude oil into components according to molecular size by distillation.

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20
Q

Name two major components of liquid petroleum gas

A

propane

butane

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21
Q

Mention the three processes by which octane is converted to various other substances

A

catalytic cracking

dehydrocyclisation

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22
Q

How wold you expect the boiling points of petrol and diesel to compare ?

A

Diesel has a higher boiling point.

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23
Q

Identify the hydrocarbon gas produced by anaerobic bacterial decomposition of either animal waste or vegetation.

A

Methane

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24
Q

Give a major use of methane

A

production of fertilizer

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25
Q

Why is the concentration of methane in the air a cause of concern ?

A

global warming

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26
Q

Why do high molecular mass alkanes have high boiling points ?

A

Because they have stronger intermolecular forces between them.

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27
Q

What is the purpose of dehydrocyclisation in oil refining ?

A

To make more efficient fuel.

To increase the octane rating.

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28
Q

But-2-ene, 2-methylbutane and a second alkene were the products of catalytic cracking of a dodecane. Deduce the molecular formula of the second alkene.

A

C3H6

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29
Q

Name 2 metals which act as catalyst in the catalytic converters of modern cars

A

Palladium
Platinum
Rhodium

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30
Q

Define heat of combustion ?

A

This is the energy released when one mole of a substance is burned in excesss oxygen.

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31
Q

Give a use of residue

A

roofing
road making
waterproofing

32
Q

Name the oil refining process that converts octane into 2,2,4- trimethylpentane

A

Isomerisation

33
Q

Name the oil refining process that converts benzene into ethylbenzene

A

dehydrocyclisation

reforming

34
Q

State an advantage of isomerisation and dehydrocyclisation.

A

This improves octane rating and reduces tendency of fuel to cause knocking.

35
Q

propene and octane were the products of catalytic cracking of C18H38. Deduce the molecular formula of the third product.

A

C7H14

36
Q

Define heat of reaction ?

A

This is the heat change when the numbers of moles of reactants in the balanced equation react completely.

37
Q

In an experiment to measure the heat of reaction for the reaction between NaOH and HCl, What was the advantage of mixing the solutions in a polystyrene foam cup ?

A

Polystyrene is a good insulator and it prevents heat loss.

38
Q

What process is used to convert molecules in fractions to smaller molecules that are in greater demand ?

A

Catalytic Cracking.

39
Q

Give two advantages of adding oxygenates such as ethanol to petrol.

A

To increase the octane number.

To reduce pollution

40
Q

Give 2 properties of hydrogen that makes it the fuel of choice for the space shuttle.

A

Low molecular mass
Eco-friendly
High octane number

41
Q

State one disadvantage of hydrogen as a fuel.

A

Explosive
Expensive
Leaks easily out of containers
Hazardous

42
Q

Give 2 ways that hydrogen gas is produced industrially.

A

Dehydrocyclisation
Co-product of catalytic cracking
Electrolysis of water

43
Q

What observation is made when a sample of ethanal is heated with feeling’s reagent ?

A

The colour changes from blue to red

44
Q

State one advantage of hydrogen as a fuel.

A

Clean and Renewable

45
Q

What is catalytic cracking ?

A

This is the splitting of long chain molecules by the action of heat and catalysts to give short chains.

46
Q

Why are lead compounds unsuitable as additives for petrol use in modern cars?

A

It destroys the catalytic converter.

It has poisonous emissions.

47
Q

Explain why the substance MTBE is sometimes added to motor fuel.

A

To increase its octane number

48
Q

Name the substance that was previously added to motor fuel.

A

Lead

49
Q

Name the lab apparatus used to measure the heats of combustion of fuels and foodstuffs.

A

The Bomb Calorimeter.

50
Q

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

A

They are hydrocarbons

51
Q

Give the major use of light gasoline and naphtha

A

To make petrol.

52
Q

Why is catalytic cracking carried out ?

A

To give products with a higher octane number.

53
Q

State 2 methods by which large quantities of hydrogen can be obtained from water

A

Electrolysis

Steam reforming

54
Q

What 2 properties of compounds are responsible for them being found in the same fraction ?

A

similar boiling points

similar molecular mass / carbon mass

55
Q

What is meant by auto ignition in petrol engines ?

A

Tendency to premature ignition.

56
Q

Define bond energy.

A

This is the average energy required to break a bond and to separate the atoms into separate single atoms in the gaseous state.

57
Q

Define hydrocarbons

A

These are compounds of carbon and hydrogen only .

58
Q

Define structural isomers

A

These are compounds with the same molecular formula but different structural formulas.

59
Q

Explain why some of the kerosene produced in oil refining is subjected to catalytic cracking.

A

Its chains are too long.

60
Q

Name 2 processes carried out in oil refineries to modify hydrocarbon structures.

A

Isomerisation

Dehydrocyclisation

61
Q

What structural feature of 2,2,4-trimethylpentane gives it such a high octane number ?

A

Its branching

62
Q

What 2 changes to the hydrocarbon occurs during dehydrocyslisation ?

A

loss of a hydrogen

ring formation

63
Q

Give an example of an oxygenate

A

methanol
butanol
ethanol

64
Q

Give two reasons why oxygenates are added to petrol

A

To increase its octane number.

Makes it more eco friendly

65
Q

In which fraction does pentane belong ?

A

Light gasoline

66
Q

Write a balanced equation for the combustion of pentane in excess oxygen.

A

C5H12 + 8O2 = 5CO2 + 6H20

67
Q

How do the molecules of the naphtha fraction differ from the molecules of the gas ?

A

Naphtha have shorter chains.

68
Q

Give a use of bitumen

A

Roofing
Waterproofing
Road surfacing

69
Q

What is an economic importance of catalytic cracking in oil refining ?

A

It provides the products needed for petrol.

70
Q

Why is the use of benzene in petrol strictly controlled ?

A

Benzene is carcinogenic

71
Q

Give 2 reasons why lead is no longer added to petrol

A

It is poisonous

It poison the catalyst in catalytic converter.

72
Q

Give two properties of methane which account for its usefulness as a fuel

A

It is non toxic.
It is cheap
It can be easily distributed
It is plentiful

73
Q

What doe LPG stand for ?

A

Liquid petroleum gas

74
Q

Name a major source from which methane os released into the atmosphere.

A

Anaerobic decay
Animals
Compost
Fossil fuels

75
Q

Explain why it is possible to measure experimentally the heats of formation of CO2 and H2O but not that of ethaonic acid.

A

Ethaonic acid cannot be formed directly from elements.

The formation of ethaonic acid is not a combustion reaction.

Chemistry 101 (3 decks)

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