Fuels & heats and organic defn

Question 1

hydrocarbon

Answer 1

compound that contains carbon and hydrogen only

Question 2

What is a saturated compound

Answer 2

one in which there are only single bonds between the atoms in the molecule

Question 3

What are the first 8 names for organic families

Answer 3

1 carbon - meth 
2- eth 
3 - prop 
4 - but 
5 - pent 
6- hex 
7 - hep 
8 - oct

Question 4

what is the formula for alkanes

Answer 4

Cn H2n+2

Question 5

What is a homologous series

Answer 5

group of compounds that contain the same -
functional group
general formula
each successive member differs by a CH2

Question 6

what are (structural) isomers

Answer 6

compounds with the same molecular formula but different structural formulas

Question 7

What is the physical properties of alkanes

Answer 7

first 4 are gases , higher alkanes are liquids
insoluble in water
soluble in non-polar solvent - cyclohexane

Question 8

what is an unsaturated compound

Answer 8

one that contains one or more double or triple bonds between the atoms in the molecule

Question 9

what is an aliphatic compound

Answer 9

an organic compound that consists of straight or branched chains of carbon atoms, or rings of carbon atoms other than benzene

Question 10

what is an aromatic compound

Answer 10

compounds that contain a benzene ring structure in their molecules

Question 11

What are mercaptans

Answer 11

sulfur compounds added to natural gas and LPG

strong smell so it can be detected in leaks

Question 12

what is fractional distillation

Answer 12

a mixture of different liquids is separated into different components depending on their boiling points

Question 13

what substances come from the fractional distillation of crude oil and what are their uses

Answer 13

Refinery gas - LPG (liquified petroleum gas )  
Petrol / light gasoline - petrol for cars
Naphtha 
Kerosene 
Diesel/gas oil 
Lubricating oil 
Fuel oil 
BItumen

Question 14

What is auto-ignition

Answer 14

the premature ignition of the petrol/air mixture before normal ignition of the mixture by a spark takes place

Question 15

What is the octane number of a fuel

Answer 15

octane number of a fuel is a measure of the tendency of the fuel to resist auto ignition / knocking

Question 16

Name the compounds with an octane number of 100 and 0

Answer 16

100 - 2,2,4-trimethylpentane (iso-octane)

0- heptane

Question 17

What are the factors affecting the octane number

Answer 17

chain length - shorter chains have higher
branching - the more branched the higher the octane number
cyclic structure - cyclic compounds have higher octane no. than straight chains

Question 18

what is standard petrol that has an octane number of 97 composed of

Answer 18

97% 2,2,4 trimethylpentane

3% heptane

Question 19

Why is tetraethyllead not used in petrol anymore

Answer 19

toxic

destroys catalytic converters

Question 20

What methods increase the octane number

Answer 20

isomerisation
catalytic cracking
dehyldrocyclisation
adding oxygenates

Question 21

What is isomerisation

Answer 21

a straight chained alkane with a low octane number is broken. When the chain fragments are allowed to join together again they are more likely to be branched (using heat and a catalyst )

Question 22

what does isomerisation cause

Answer 22

branching

Question 23

What is catalytic cracking

Answer 23

its where long chained molecules are cracked or broken into shorter chains which have a higher octane number, short chains tend to be branched

Question 24

What is dehydrocyclisation

Answer 24

the conversion of a straight chain alkane with a low octane no. into a ring compound with a higher octane no.
hydrogen is a by product

Question 25

What are oxygenates

Answer 25

refers to any fuel that contains oxygen in its molecule

Question 26

What is MTBE

Answer 26

methyl tertiary butyl ether

Question 27

What are the advantages of adding oxygenates to petrol

Answer 27

reduces knocking (ie. increase octane number)
oxygen additives reduces carbon monoxide during burning of the fuel

Question 28

What are the uses of hydrogen gas

Answer 28

manufacture of ammonia

hydrogenating vegetable oil to make margarine

Question 29

What are the methods for manufacturing hydrogen gas on a large scale

Answer 29

Steam reforming of natural gas

electrolysis of water

Question 30

Why is hydrogen not used more as a fuel

Answer 30

forms an explosive mixture with air - hard to store and transport

Question 31

What is an exothermic reaction

Answer 31

a reaction that gives out heat to its surroundings (delta H = -)

Question 32

What is an endothermic reaction

Answer 32

a reaction that takes in heat from the surroundings (delta H = + )

Question 33

What is the heat of reaction

Answer 33

heat change in kilojoules released or absorbed when the number of moles of reactants in the balanced equation react completely

Question 34

What is the bond energy

Answer 34

the energy required to break 1 mole of covalent bonds and to separate the neutral atoms completely from each other

Question 35

What is the heat of combustion

Answer 35

heat change that takes place when 1 mole of a substance is burned im excess oxygen

Question 36

What is the kilogram calorific value of a fuel

Answer 36

the heat energy produced when 1kg of the fuel is completely burned in excess oxygen

Question 37

What is the heat of formation

Answer 37

the heat change that takes place when 1 mole of a compound is formed from its elements in their natural/standard states

Question 38

What is the law of conservation of energy

Answer 38

energy cannot be created or destroyed but can only be converted from one form of energy to another

Question 39

What is Hess’s Law

Answer 39

the heat change for a given reaction depends on the initial and final stages and is independent of the path followed