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Chemistry - a level > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

what are alkanes

A

saturated hydrocarbons

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2
Q

what is a hydrocarbon

A

contains hydrogen and carbon only

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3
Q

what does it mean by saturated

A

each carbon is bonded 4 times with the maximum number of hydrogens possible

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4
Q

what do cycloalkanes have

A

2 hydrogens per carbon
saturated
functional group isomer of alkenes

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5
Q

where are alkanes found

A

in crude oil which is a mixture of different length of hydrocarbons

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6
Q

how is crude oil vapourised

A

using a furnace to 350 degrees

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7
Q

what does the vapourised oil do once it enters the column

A

it rises through the trays
the longest hydrocarbons don’t vaporise and run down to the bottom

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8
Q

describe the temperature gradient in a fractioning column

A

cooler at the top
as the vapour rises parts of the mixture condense at different temperatures
due to the different chain lengths = different bp
fractions are drawn at different levels

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9
Q

what happens to shortest hydrocarbons

A

they don’t condense at 20 degrees so come off as a gas at the top of the column

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10
Q

what is cracking

A

breaking longer chain alkane into shorter hydrocarbons

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11
Q

what are the two types of cracking

A

thermal and catalytic

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12
Q

what are the conditions for thermal cracking

A

high temperature of 1000 degrees and 70 atm pressure

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13
Q

what is the main products of thermal cracking

A

alkenes

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14
Q

what are alkenes used to make

A

polymers
e.g. plastic

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15
Q

what are the conditions for catalytic cracking

A

slight pressure
high temperature of 450 degrees
a zeolite catalyst is used to help lower the temperature needed

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16
Q

what are the products of catalytic cracking

A

aromatic hydrocarbons
useful for fuel in vehicles

17
Q

what does a zeolite catalyst do

A

lowers temperature and pressure so cracking can occur
lowers costs and speeds up process

18
Q

complete combustion of alkanes

A

burn in oxygen completely to form co2 and h2o

19
Q

what is the incomplete combustion of alkanes

A

alkanes burn with a limited 02 supply it produces carbon monoxide (CO) and carbon (soot)

20
Q

why is carbon monoxide dangerous

A

-poisonous
-it binds to haemoglobin in the blood preventing oxygen bonding
-carbon monoxide can be removed using a catalytic converter

21
Q

what does burning fossil fuels do

A

produces co2 = greenhouse gas

22
Q

what is the greenhouse effect

A

co2 absorbs infrared radiation (heat) from the sun
but it emits some of it back to earth = greenhouse effect

23
Q

what does ozone cause

A

photochemical smog which harms the respiratory system

24
Q

where does ozone occur

A

in the lowest levels of the atmosphere
exists as sunlight, hydrocarbon and nitrogen dioxide and mixes to form ozone (toxic)

25
Q

when are oxides of nitrogen made

A

when oxygen and nitrogen are found in the air combine under high pressure and temperature

26
Q

what do catalytic converters do

A

reduce the amount of unburnt hydrocarbons and oxides of nitrogen going into the atmosphere

27
Q

what is wet scrubbing

A

it helps remove so2 from flue gases
this is where an alkali is used to neutralise sulphur dioxide from flue gases

28
Q

what does a chain reaction involve

A

initiation
propagation
termination

29
Q

what is initiation

A

radicals produced normally using visible light or ultraviolet
= photochemical reactions / photodissociation
the bond breaks equally producing 2 highly reactive radicals

30
Q

what is propagation

A

when a radical reacts with a non radical molecule
new radicals are created and then go on to react with other non-radicals = chain reaction

31
Q

what is termination

A

when 2 radicals react to form a stable non radical molecule
this ends the chain reaction hence termination

Chemistry - a level (14 decks)

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