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alkanes Flashcards

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1
Q

what are alkenes

A

Alkenes are ​unsaturated hydrocarbons​ meaning they contain a carbon-carbon double bond

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2
Q

what does saturated mean

A

Compounds contain single bonds only

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3
Q

what is the general formula for an alkane

A

CnH2n+2

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4
Q

why does the boiling point of alkanes increases with increasing C chain length

A

· Alkanes have induced dipole-dipole attractions between molecules

· Strength of attractions increases with increasing size of molecule and number of electrons

· The longer the C chain, the bigger the molecule and the more electrons

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5
Q

2,2-dimethyl propane and pentane both have the same number of electrons, but pentane has a higher boiling point. This is because:

A

· 2,2-dimethyl propane has more branches than pentane

· There is more surface contact between molecules of pentane than molecules of 2,2-dimethyl butane

· The induced dipole-dipole attractions between molecules of pentane are stronger

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6
Q

what is a fraction

A

A mixture of compounds with similar boiling points and similar sized molecules

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7
Q

what is crude oil

A

Crude oil is a mixture of hydrocarbons with different chain lengths

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8
Q

what is fractional distillation used for

A

Fractional distillation is used to separate hydrocarbons based on their differing boiling points, which is determined by their C chain length

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9
Q

describe how crude oil is separated into fractions using fractional distillation

A

· Crude oil is heated to vapourise it so everything is at a gaseous state and enters the column

· Hydrocarbons have different boiling points

· Boiling point depends on size/Mr/chain length

· The column is cooler at top and hotter at the bottom (temp gradient)

· Larger molecules with higher boiling points condense at the bottom

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10
Q

why is cracking used

A

breaks the larger fractions (for which supply exceeds demand) into smaller fractions (for which demand exceeds supply and also makes alkenes

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11
Q

what does thermal cracking produce

A

always produces one alkane, with all other molecules being alkenes

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12
Q

what does catalytic cracking produce

A

high percentage of branched alkanes and cycloalkanes.

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13
Q

what are the conditions for thermal cracking

A

high temperatures and high pressures

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14
Q

what are the conditions for catalytic cracking

A

high temperatures
slight pressures
a catalyst - zeolite crystal

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15
Q

what are the conditions for complete combustion

A

plentiful supply of oxygen

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16
Q

give a equation for complete combustion of nonane

A

C9H20 + 14O2 → 9CO2 + 10H2O

17
Q

give 2 possible products of incomplete combustion

A

carbon monoxide gas or solid carbon (soot) + water

18
Q

state chemicals are produced during combustion and give their polluting effect

A

CO2 Greenhouse gas

H2O Greenhouse gas

CO Poisonous

Solid C Damages the lungs/ exacerbates asthma

19
Q

give the equation for how sulfur dioxide is formed when Sulphur impurities are burnt

A

S(s) + O2(g) →SO2(g)

20
Q

give the equation for the formation of acid rain (from Sulphur impurities)

A

SO2(g) + 0.5 O2(g) + H2O(l) → H2SO4(l)

21
Q

what gas dissolves in rainwater form acid rain

A

SO2 (or HNO3)

22
Q

how are oxides of nitrogen formed

A

the high temperatures in the car engines cause some of the nitrogen to react with the oxygen to produce oxides of nitrogen

23
Q

give the equation for the formation of acid rain (from nitrogen dioxide)

A

4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(g)

24
Q

some unburnt hydrocarbons are toxic if breathed in give an example

A

C8H18

25
Q

what is Flue Gas Desulphurisation

A

the process of removing sulphur dioxide gas is called flue gas desulfurisation.

26
Q

what is the equation for the desulfurisation with CaO

A

Cao + SO2 → CaSO3

27
Q

what is the equation for the desulfurisation with CaCO3

A

CaCO3 + SO2 → CaSO4 + CO

28
Q

how does a catalytic converter withstand high temperatures

A

its made of ceramic which withstands the pressure

29
Q

describe the structure and function of a catalytic converter

A

has a honeycomb structure made of platinum or rhodium metal which are catalysts
honeycomb structure increases the surface area, increasing the reaction rate of the reactions:

30
Q

what is the equation for the removal of carbon monoxide and nitrogen monoxide

A

2NO(g) + 2CO(g) →N2(g) + 2CO2(g)

31
Q

what is the equation for the removal of unburned hydrocarbons and nitrogen monoxide

A

C8H18 + 25NO→ 8CO2 + 9H2O + 12.5N

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