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Chemistry 3.3 Organic chemistry > alkanes > Flashcards

alkanes Flashcards

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1
Q

why are alkane molecules non-polar?

A

C and H have very similar electronegativities so form non-polar bonds

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2
Q

how are neighbouring alkane molecules attached to each other?

A

by Van Der Waals’ forces- weak intermolecular forces

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3
Q

describe alkane solubility in water?

A

hydrogen bonds between water molecules are much stronger than the Van Der Waals’ in alkanes so they are insoluble in water

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4
Q

the longer the carbon chain the…..

A

higher the bp

higher the viscosity

lower the flammability

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5
Q

why does the bp increase for longer chain alkanes?

A

-more SA (only talk about this for straight chains not branched)
-larger molecule
-greater number of electrons

SO more and stronger VDW forces between molecules = more energy to overcome

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6
Q

what is the general formula for alkanes?

A

Cn H2n+2

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7
Q

what is a hydrocarbon?

A

a compound containing hydrogen and carbon atoms only

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8
Q

are alkanes saturated or unsaturated, why?

A

saturated
only single bonds between carbon atoms

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9
Q

what is the general formula for cycloalkanes?

A

Cn H2n

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10
Q

what is crude oil/ petroleum?

A

a mixture consisting mainly of alkane hydrocarbons and it is our main source of fuels and petrochemicals

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11
Q

what is a mixture?

A

more than one different compounds or elements not chemically bonded together

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12
Q

what is fractional distillation?

A

the separation of the components of a liquid into fractions which differ in boiling points

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13
Q

what is a fraction?

A

a group of components that have similar boiling points and are removed at the same level in the fractionating column

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14
Q

explain why branched alkanes have a lower boiling point?

A

more branched means less SA which means there are less points of contact where VDW’s can form

less VDW formed and weaker VDW = less energy to overcome

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15
Q

when can we only use the assumption that branched alkanes have a lower boiling point?

A

when they have a similar Mr and so are similar in size

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16
Q

describe the process of fractional distillation?

A

-vaporise crude oil in the furnace so the vapor can rise up the column
-the top of the column is cooler than the bottom
-larger, longer hydrocarbons condense at the bottom of the column, shorter, smaller hydrocarbons condense at the top of the column

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17
Q

which two fractions don’t vaporise or condense?

A

bitumen has too high of a boiling point to vaporise so leaves at the bottom as a liquid

petroleum gas doesn’t condense so leaves the top of the column as a gas

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18
Q

what are the two types of cracking?

A

thermal and catalytic

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19
Q

how is cracking achieved?

A

by breaking C-C bonds, producing shorter chain hydrocarbons from longer chain hydrocarbons

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20
Q

why do we do cracking?

A

we have a lower supply and higher demand for shorter hydrocarbons

we have a higher supply and lower demand for longer hydrocarbons

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21
Q

what are the conditions for thermal cracking?

A

very high pressures and very high temperatures

22
Q

what does thermal cracking produce?

A

alkanes and a high percentage of alkenes

23
Q

how are mixtures of products produced in thermal cracking?

A

the C-C bonds can break at different positions in the carbon chain

24
Q

what are the products of thermal cracking used to make?

A

polymers (mainly alkenes)

25
Q

what conditions are needed for catalytic cracking?

A

high temperature, slight pressure and in the presence of a zeolite catalyst

26
Q

what does catalytic cracking produce?

A

cycloalkanes and branched alkanes as well as aromatic hydrocarbons such as benzene

27
Q

what are the products of catalytic cracking used as?

A

motor fuels

28
Q

how is energy obtained from alkane fuels?

A

when they are combusted
products formed in the reaction depend on the supply of oxygen

29
Q

what is the equation for complete combustion?

A

alkane + oxygen ——> carbon dioxide + water

30
Q

when does incomplete combustion occur?

A

limited supply of oxygen

31
Q

what is the equation for incomplete combustion?

A

alkane + oxygen ———> carbon monoxide + water

32
Q

what is the equation for further incomplete combustion?

A

alkane + oxygen ——-> solid carbon (soot) + water

33
Q

when does further incomplete combustion occur?

A

very limited supply of oxygen

34
Q

name pollutants we need to know about?

A

unburnt hydrocarbons
carbon dioxide
carbon monoxide
carbon
nitrogen oxides
sulfur dioxide

35
Q

how do unburnt hydrocarbons produce low level ozone?

A

reacts with NOx gases to form low level ozone

36
Q

what are the effects of the pollutants unburned hydrocarbons?

A

leads to low level ozone which causes respiratory problems

global dimming

37
Q

what is the effect of carbon dioxide and how is it produced?

A

global warming

combustion of fuels

38
Q

what is the effect of carbon monoxide and how is it produced?

A

toxic gas

incomplete combustion of fuels in a limited supply of oxygen

39
Q

what can carbon (soot) lead to, and how is it produced?

A

particles lead to asthma

incomplete combustion of fuels in a limited supply of oxygen

40
Q

what is the effect of nitrogen oxides and how are they produced?

A

acid rain and photochemical smog

N2 and O2 from the air react at high temps in engines

41
Q

what is the effect of sulfur dioxide and how is it produced?

A

acid rain

S from fuel impurities reacts with O2 in the air

42
Q

what has been fitted in most cars to remove unburnt CO and NO hydrocarbons?

A

catalytic converters

43
Q

write an equation for how a catalytic converter removes unburnt hydrocarbons?

A

2CO + 2NO ——-> 2CO2 + N2

44
Q

what structure do catalytic converters contain?

A

honeycombed structure coated with a thin layer of Pt, Pd, Rh metals

45
Q

why is a thin layer of metals used in catalytic converters?

A

to reduce the amount needed (reduce cost)

46
Q

what does the honeycomb structure of a catalytic converter provide?

A

a large surface area

47
Q

what reacts to produce less polluting products?

A

NO and CO

2NO + 2CO ——–> 2CO2 +N2

48
Q

what are the two ways of removing unburnt hydrocarbons?

A

reaction with oxygen
reaction with NO

49
Q

what is produced which requires flue gas desulfurisation?

A

power stations burn coal or natural gas to produce electricity. Sulfur dioxide is also produced and this needs to be removed

50
Q

what are chimneys or flues coated with to react with sulfur dioxide produced?

A

calcium oxide or calcium carbonate which absorb and react with it

SO2 + CaO ——–> CaSO3
SO2 + CaCO3 ——–> CaSO3 + CO2

51
Q

what is the test for the presence of an alkene?

A

bromine water turns from orange to colourless

Chemistry 3.3 Organic chemistry (5 decks)

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