Fuels & Thermochemistry Flashcards by Fareedah Omotayo

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

They are sulphur compounds.

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

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

2,2,4-trimethylpentane and heptane

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Define heat of Combustion

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

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Define steam reforming

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

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What is the balanced equation for for steam reforming?

CH4 + H20 = 3H2 + CO2

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

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

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State a disadvantage of using hydrogen as a fuel.

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

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

Ammonia
Hydrogen sulfide
Phosphine

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

Kerosene

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Define octane number.

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

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

A short chain
Highly branched
Cyclic structure.
Aromatic

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Define homologous series

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

methanol

ethanol

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

Fractional distillation

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Name a fraction with the carbon chain lengths to form petrol

Light gasoline

Naphtha

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Name a fraction used to obtain bitumen

Residue

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Write a balanced equation for the dehyldrocyclisation of hexane

C6H14 = C6H12 + H2

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

Catalytic Cracking

Isomerisation

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What is the fractionation of crude oil

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

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Name two major components of liquid petroleum gas

propane

butane

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

catalytic cracking

dehydrocyclisation

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

Diesel has a higher boiling point.

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

Methane

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Give a major use of methane

production of fertilizer

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

global warming

Why do high molecular mass alkanes have high boiling points ?

Because they have stronger intermolecular forces between them.

What is the purpose of dehydrocyclisation in oil refining ?

To make more efficient fuel. | To increase the octane rating.

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.

C3H6

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

Palladium Platinum Rhodium

Define heat of combustion ?

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

Give a use of residue

roofing road making waterproofing

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

Isomerisation

Name the oil refining process that converts benzene into ethylbenzene

dehydrocyclisation | reforming

State an advantage of isomerisation and dehydrocyclisation.

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

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

C7H14

Define heat of reaction ?

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

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 ?

Polystyrene is a good insulator and it prevents heat loss.

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

Catalytic Cracking.

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

To increase the octane number. | To reduce pollution

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

Low molecular mass Eco-friendly High octane number

State one disadvantage of hydrogen as a fuel.

Explosive Expensive Leaks easily out of containers Hazardous

Give 2 ways that hydrogen gas is produced industrially.

Dehydrocyclisation Co-product of catalytic cracking Electrolysis of water

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

The colour changes from blue to red

State one advantage of hydrogen as a fuel.

Clean and Renewable

What is catalytic cracking ?

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

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

It destroys the catalytic converter. | It has poisonous emissions.

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

To increase its octane number

Name the substance that was previously added to motor fuel.

Lead

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

The Bomb Calorimeter.

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

They are hydrocarbons

Give the major use of light gasoline and naphtha

To make petrol.

Why is catalytic cracking carried out ?

To give products with a higher octane number.

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

Electrolysis | Steam reforming

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

similar boiling points | similar molecular mass / carbon mass

What is meant by auto ignition in petrol engines ?

Tendency to premature ignition.

Define bond energy.

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

Define hydrocarbons

These are compounds of carbon and hydrogen only .

Define structural isomers

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

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

Its chains are too long.

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

Isomerisation | Dehydrocyclisation

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

Its branching

What 2 changes to the hydrocarbon occurs during dehydrocyslisation ?

loss of a hydrogen | ring formation

Give an example of an oxygenate

methanol butanol ethanol

Give two reasons why oxygenates are added to petrol

To increase its octane number. | Makes it more eco friendly

In which fraction does pentane belong ?

Light gasoline

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

C5H12 + 8O2 = 5CO2 + 6H20

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

Naphtha have shorter chains.

Give a use of bitumen

Roofing Waterproofing Road surfacing

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

It provides the products needed for petrol.

Why is the use of benzene in petrol strictly controlled ?

Benzene is carcinogenic

Give 2 reasons why lead is no longer added to petrol

It is poisonous | It poison the catalyst in catalytic converter.

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

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

What doe LPG stand for ?

Liquid petroleum gas

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

Anaerobic decay Animals Compost Fossil fuels

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

Ethaonic acid cannot be formed directly from elements. | The formation of ethaonic acid is not a combustion reaction.