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Chemistry #2 > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

give a description of alkanes

A

they are a homologous series of saturated hydrocarbons with the general formula CnH2n+2

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2
Q

are alkanes reactive

however?

A

alkanes are very unreactive

however they burn in oxygen (combustion) and react with halogens to form halogenoalkanes

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3
Q

what happens to BP of alkanes as chain length increases and why?

A

boiling point increase as chain length increases because greater surface area contact and therefore more van der waal forces between molecules

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4
Q

what happens to BP as alkanes get more branched

A

BP decreases because they have less surface area contact between molecules and fewer van der waals forces between molecules

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5
Q

what is crude oil

A

crude oil is a complex mixture consisting mainly of alkanes (including cycloalkanes) aromatic compounds and others containing S,O,N.

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6
Q

is crude oil useful in its raw form ?

how does it become useful

A

no

by getting separated in fractional distillation

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7
Q

what is distillation

A

distillation is a method to separate mixtures of miscible liquids where separation is based on boiling point

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8
Q

list the essential features of fractional distillation of crude oil

A

1) crude oil is vaporised

2) the vapour is passed into a tower which is hotter at the bottom and cooler at the stop

3) as the vapour rises it cools

4) molecules will condense at different points as they have different boiling points

5) the larger the molecule the further down it condenses

6) this produces fractions ( a fraction is a mixture of hydrocarbons with similar boiling points

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9
Q

the boiling point of the alkanes increases as the strength of the van der waal forces increases . this is increased bevause:

A

increased mr
increased surface area contact

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10
Q

as the carbon chain gets longer, the hydrocarbons:

A

get more viscous

less flammable

less volatile

have higher BP

stronger van der waal forces between molecules

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11
Q

how do we supply demand for shorter hydrocarbons

A

longer hydrocarbons are cracked

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12
Q

what is cracking

A

cracking is the:

breaking of long chain alkane molecules into smaller ones

it involves breaking a strong C-C bond

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13
Q

what is naptha

A

short chain hydrocarbons (C7-C14)

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14
Q

why do we carry out cracking reactions

A

1) short chains are higher in demand economically

2) alkenes are used to make plastics and polymers

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15
Q

what are the 2 types of cracking

A

thermal and catalytic

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16
Q

describe thermal cracking

A

high temperature

high pressure

produces a high percentage of alkenes and straight chain alkanes

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17
Q

describe catalytic cracking

A

high temperature

moderate presssure

zeolite catalyst

produces branched alkanes (motor fuels) , cycloalkanes and aromatic hydrocarbons

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18
Q

why are alkanes used as fuels

A

they will burn

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19
Q

what is complete combustion

A

alkanes reacting with excess of oxygen

20
Q

what is produced in complete combustion

A

alkane + oxygen —> carbon dioxide and water

21
Q

which is more exothermic complete or incomplete combustion

A

complete

22
Q

what’s incomplete combustion

A

reacting with limited oxygen

23
Q

what’s produced in incomplete combustion

A

carbon monoxide CO (toxic gas)

carbon C (black solid

24
Q

what’s produced in incomplete combustion

A

carbon monoxide CO (toxic gas)

carbon C (black solid)

and water

25
Q

what other pollutants are made in internal combustion engines

A

NO or NO2

unburnt hydrocarbons

26
Q

what other pollutants are made in coal burning power stations

A

SO2

27
Q

how do we reduce the problem of carbon monoxide

A

use catalytic converters in cars

28
Q

how do we reduce the problem of unburnt hydrocarbons

A

use catalytic converters in cars

29
Q

how do we reduce the problem of NO/NO2

A

use catalytic converters in cars

30
Q

what’s the problem with C carbon particulates

A

can cause respiratory problems

31
Q

what’s the problem with unburnt hydrocarbons

A

photochemical smog

32
Q

what’s the problem with NO/NO2

A

reacts with water to form acid rain

33
Q

how is NO NO2 formed

A

combustion of N2 in the air and O2 in the air at very high temperatures in engines and furnaces

34
Q

what’s the problem with sulfur dioxide

A

reacts with water to form acid rain

35
Q

how to reduce problem of SO2

A

flue gas desulfurisation

36
Q

what neutralises SO2

A

CaO and CaCO3 (bases)

37
Q

where are sulfur compounds found

A

in coal and crude oil

38
Q

how is SO2 formed

A

by burning of sulfur compounds

39
Q

why are high temperatures needed to produce NO2

A

to break the strong triple bond between nitrogen atoms

40
Q

name all the components of the catalytic converter

A

1) honey comb structure

2) made ceramic material

3) thin coating of metal catalyst ( rhodium palladium platinum)

41
Q

why honey comb structure

A

increase surface area and cost effective

42
Q

why ceramic material

A

withstands high temperatures of combustion engine

43
Q

why thin coating of metal catalyst ( rhodium platinum palladium)

A

to reduce cost and increase surface area

44
Q

what happens when dangerous gases pass over the catalyts

give example

A

the dangerous gases react together to produce less harmful gasses

2CO + 2NO —> 2CO2 and N2

45
Q

give equation for formation of acid rain

A

4NO2 + 2H2O + O2 —> 4HNO3

Chemistry #2 (8 decks)

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