fuels and heats of reactions

Question 1

organic chemistry is….

Answer 1

the study of compounds of carbon

Question 2

hydrocarbons are

Answer 2

compounds containing only hydrogen and carbon

Question 3

what are fossil fuels?

Answer 3

fuels made from remains of plants and animals that lived millions of years ago

Question 4

saturated compound

Answer 4

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

Question 5

homologous series

Answer 5

series of compounds of similar chemical properties
showing gradations in physical properties, having a general formula for its members, each having a similar method of preparation, each member differs from the previous by (CH2) unit

Question 6

what are structural isomers

Answer 6

compounds with the same molecular formula but different chemical formulas

Question 7

whats an unsaturated compound

Answer 7

contains one or more double or triple binds in its molecule

Question 8

what dehydrating agent is used in the production of ethene

Answer 8

aluminium oxide

Question 9

what type of reaction is the production of ethene from ethanol

Answer 9

dehydration/ elimination reaction

Question 10

in dehydration of ethanol whats role of glass wool

Answer 10

holds ethanol in place

Question 11

why is delivery tube removed from water before the bunsen burner is turned off

Answer 11

to prevent suck back which could crack the class wear

Question 12

describe ethene gas prepared

Answer 12

colourless gas with sweetish smell

Question 13

why is it possible to collect ethene by displacement over water

Answer 13

ethene is insoluble in water

Question 14

what is observed when a lit taper is held over yest tube containing ethene
and when lime water is added to test tube

Answer 14

yellow luminous flame , slightly smoky

lime water turns milky

Question 15

how to test for saturation in ethene

Answer 15

potassium permanganate decolourises (purple to colourless)

bromine water turns from red to colourless

Question 16

use of ethene

Answer 16

ripening fruit

Question 17

use of ethyne

Answer 17

welding and cutting

Question 18

how is ethyne prepared

Answer 18

reacting water with calcium carbide- usually contaminated with calcium sulfide, calcium phosphate or calcium nitride therefore purified by bubbling through acidified copper ll sulfate

Question 19

safety precaution in preparation of ethyne

Answer 19

no naked flame brought anywhere near gas preparation apparatus-perform all tests well away from preparation apparatus

Question 20

describe calcium carbide

Answer 20

grey black solid

Question 21

whats absorbed when water is added to flask containing calcium carbide in preparation of ethyne

Answer 21

fizzing takes place in the jar, bubbles of gas start to collect in gas jar, buchner flask becomes warm

Question 22

describe ethyne gas

Answer 22

sweetish smell, colourless gas

Question 23

what is observed when lit taper is held over the mouth of a tt containing ethyne gas

Answer 23

burns with luminous smoky flame, great deal of soot is produced - more luminous and more smoky than that observed with ethene

Question 24

why is soot formed

Answer 24

as a result of the unburnt carbon

Question 25

what is an aliphatic compound

Answer 25

an organic compound consisting of open chains of carbon compounds and closed chains that resemble them in chemical properties

Question 26

aromatic compounds

Answer 26

compounds containing a benzene ring structure in their molecules

Question 27

discuss reactivity bond lengths of benzene

Answer 27

very unreactive | bonds in benzene are an intermediate between single and double bonds

Question 28

describe electrons in bezene ring

Answer 28

delocalised, free to move around hexagon, providing extra stability and explaining its unreactivity

Question 29

auto ignition

Answer 29

is the premature ignition of the petrol air mixture before normal ignition of the spark takes place ( knocking)

Question 30

what is the octane number of a fuel

Answer 30

the measure of fuels tendency to resist knocking

Question 31

what are the 3 factors affecting octane number

Answer 31

1. length on chain, shorter the chain the higher the octane number 2. degree of branching, the more branched the chain the higher the octane number 3. straight chain or cyclic structure, cyclic compounds have higher octane numbers

Question 32

isomerisation

Answer 32

changing straight chain alkanes into their isomers heated in the presence of a suitable catalyst causing chains to break chains are then allowed to join together final product is likely to be branched branched isomers and straight chain compounds are separated the straight chain compounds are recycled this increases octane number

Question 33

catalytic cracking

Answer 33

is the breaking up on long chain hydrocarbon molecules by the action of heat and catalysts into short chain molecules for which there is a greater demand

Question 34

dehydrocyclinisation

Answer 34

use of catalysts to form ring compounds

Question 35

adding oxygenates

Answer 35

eg mtbe, methanol, ethanol very little pollution cleaner fuel increased octane number

Question 36

production of hydrogen

Answer 36

steam reforming of natural gas- reacting methane with steam in the presence of a suitable catalyst electrolysis

Question 37

heat of reaction

Answer 37

the heat change when the number of moles indicated in the balanced chemical equation react completely

Question 38

heat of combustion

Answer 38

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

Question 39

kilogram calorific value

Answer 39

the heat energy produced when 1kg of a fuel is completely brned in oxygen, measured using bomb calorimeter

Question 40

bond energy

Answer 40

the average energy required to break one mole of a particular covalent bond and to separate the two neutral atoms from each other

Question 41

heat of neutralisation

Answer 41

the heat change when one mole of H(plus) ions from an acid react with one mole of OH- ions from a base

Question 42

heat given out formula

Answer 42

=mass x specific heat capacity x rise in temperature

Question 43

heat of formation

Answer 43

the heat change when one mole of a compound in its standard state is made from its elements in their standard state

Question 44

hess´s law

Answer 44

states that i a chemical reaction takes place in a number of stages the sum of the heat changes in each individual stage is equal to the total heat change if the reaction was carried out in one single stage

Question 45

law of conservation of energy

Answer 45

energy can neither be created or destroyed, only converted from one form to another