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alkanes Flashcards

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1
Q

is an alkane saturated or unsaturated? and are they reactive?

A

saturated, no

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2
Q

explain the polarity of an alkane? and therefore the forces that act

A

almost non polar because electronegativity of C and H are very similar so its only van Der Waals forces that act

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3
Q

explain the B.P.T trends of an alkane?

A

as chain length increases, b.p.t increases due to stronger van der waals forces which take more energy to break

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4
Q

explain how does branching affect the b.p.t?

A

more branching = lower b.p.t because unlike straight chians, they cant pack as clos together so van der waals forces arn’t as effective

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5
Q

explain the solubility of an alkane?

A

insoluble in water because water molecules are held together by hydrogen bonds which are much stronger than van der waals and alkanes cant form hydrogen bonds

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6
Q

what is the reactivity of an alkane?

A

reletivly unreactive because the bonds they make are strong so takes a lot of energy to break

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7
Q

what is crude oil?

A

it is a fossil feul that forms very slowly from break down of organic remains under hight pressure and temperature. there are aa mixture of different length hydrocarbons

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8
Q

explain where in the fractionating column longer hydrocarbons are collected?

A

at the base because they have a higher b.p.t and the base is the hottest

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9
Q

explain where on the fractionating colunm shorter hydrocarbons are collected?

A

near the top becasuse shorter hydrocarbons have a lower b.p.t and this is where the temperature is the coolest

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10
Q

when will hydrocarbons condense in the fractionating column?

A

they will rise until they hit a tray cooler than their b.p.t

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11
Q

what is a fraction ?

A

a mixture of hydrocarbons of similar chain length and therefore similar properties

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12
Q

how could acid rain form when burning crude oil?

A

crude oil could contain other compounds from the specimen they originated from, if sulfur is present when burned it will form sulfur dioxide, this reacts with oxygen in the air to form sulfur trioxide which will react with water in atmosphere to form sulfuric acid (acid rain)

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13
Q

write the equation for acid rain formation from sulfur

A

S+O2 —> SO2
2SO2 + O2 —–> 2SO3
SO3 + H2O ——> H2SO4

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14
Q

explain the type of process that fractional distillation is?

A

a physical process because no covalent bonds are brocken, it is only van der waals forces that are broken and reformed when heated and condensing

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15
Q

what are the 2 types of craking?

A

thermal and catalytic

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16
Q

is cracking an exo or endothermic reaction ?

A

endo

17
Q

explain the use of cracking hydrocarbons

A

longer chain fractions are not as useful because they are not as economically valuble where as shorter hydrocarbons are. so by cracking, they can meet demands

18
Q

what are the conditions for thermal cracking ?

A

700-1200 K, 7000kPa

19
Q

what happens during thermal cracking?

A

C-C bonds break homolytically, 1 electron goes to each C, 2 shorter chains are produced each ending in a C atom with an unpaired electron (free radical)

20
Q

what are the products of thermal cracking?

A

alkane and alkene of lower formulae mass

21
Q

why is an alkene produced during thermal cracking?

A

there are not enough H atoms to produce 2 alkanes so one of the new chains has to have a c=c in order to replace a H

22
Q

what are the conditions for catalytic cracking?

A

720k, lower pressure but more than 1 atm, and a zeolite catalyst

23
Q

what are the properties of a zeolite catalyst?

A

very big surface area, acidic, honeycomb structure

24
Q

what are the products created by catalytic cracking?

A

branched alkanes, cycloalkanes, aromatic alkanes, and these are all gases that can be used as motor feuls

25
Q

what is a feul?

A

substances that release heat energy when they underhgo combustion, they store a lot of energy for a small weight

26
Q

why are alkanes a good feul?

A

they burn readily and release a lot of energy but dont react with other substances

26
Q

write a balenced equation for combustion of pentane

A

C5H12 + 6.5O2 ———> 5CO2 + 3H2O

27
Q

what 6 environmental factors come with the use of alkanes as feuls ?

A

carbon monoxide production,
nitrogen oxides produced when there is enough energy to react N and O together,
sulfur dioxide production and acid rain,
carbon particulates can exacerbate asthma,
unburnt hydrocarbons are greenhouse gases,
co2 production (green house gas)

27
Q

what products are created in incomplete combustion?

A

limited supply of oxygen = carbon monoxide
even less oxygen = soot

28
Q

what is flue gas desulfurisation?

A

process of removing sulfur dioxide from gas given out by power stations

28
Q

what are the 3 stages of free radical substitution?

A

initiation, propogation, termination

28
Q

what is the word equation for radical substitution ?

A

alkane + halogen ——–> halogenoalkane + hydrogenhalide

29
Q

how is sulfur removed from flue gas?

A

a mixture of calcium oxide/ or calcium carbonate and water is sprayed on the flue gas, the calcium reacts with the sulfur to form calcuim sulphite which is oxidised to form calcium sulfate which can be sold

30
Q

what happens during the initiation stage of free radical substitution?

A

breaking of the halogen-halogen bond homolytically using UV light, creates a halogen radical

30
Q

write the formula for flue gas desulfurisation

A

CaO + H2O + SO2 + 1/2 O2————-> CaSO4

30
Q

what is the use of catalytic converters?

A

reduce output of carbon monoxide, nitrogen oxides and unburnt hydrocarbons in exahust gas

31
Q

how does a catalytic converter work?

A

gases pass over it and react with each other to form less harmful gases

32
Q

how do radicals attack ozone molecules?

A

chlorine radicals are formed when the C-Cl in a CFC breaks homolytically in the presence of UV light which then attacks ozone molecules

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