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Chemistry Year 12 > Alkanes 3.3.2 > Flashcards

Alkanes 3.3.2 Flashcards

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1
Q

What does thermal cracking mean?

A

Thermal cracking takes place at high pressure and produces a high percentage of alkenes.

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2
Q

What does catalytic cracking mean?

A

takes place at a slight pressure , high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons

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3
Q

what’s the general formula for alkanes?

A

CnH2n+2

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4
Q

Why is cracking long chain hydrocarbons into shorter hydrocarbons more useful?

A

fractions with shorter carbon chains are more in demand than larger fractions
- products of cracking are more valuable than the starting materials

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5
Q

What is the process of fractional distillation and crude oil ?

A

1) mixture is vaporised and fed into fractionating column.
2) vapours rise , cool and condense
3) products are siphoned off for different uses.

  • Products with short carbon chains = lower boiling points so they rise higher up the column before reaching their boiling point. They’re collected at the top of the column
  • products with Long carbon chains = higher boiling point so they are low down in the fractionating column. They condense and are collected at the bottom.
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6
Q

What pollutants will burning hydrocarbon - based fuels produce?

A
  • carbon monoxide
  • sulfur dioxide
  • Nitrogen oxides
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7
Q

What are flue gases?

A

Gases released from factory processes / power stations

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8
Q

How can you remove SO2 from flue gases?

A

Use calcium oxide or calcium carbonate

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9
Q

How can you remove carbon monoxide and other gaseous pollutants from internal combustion engines?

A

By using a catalytic converter.
This uses a rhodium catalyst to convert harmful products into more stable products such as CO2 or H2O

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10
Q

What is the complete combustion equation for CH4 (methane)?

A

CH4 + O2 => CO2 + 2H2O

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11
Q

What is the incomplete combustion equation for CH4 ( methane) ?

A

CH4 + 1 1/2 O2 => CO + 2H2O

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12
Q

Why does incomplete combustion happen ?

A

Not enough O2

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13
Q

Why do we use calcium oxide (CaO) to remove SO2 from flue gases ?

A

CaO is basic so will react with acid.
It’s an acid - base reaction

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14
Q

What is CaSO4 (calcium sulphate ) also known as and what can it be used for?

A

-Gypsum
- Used for plastering

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15
Q

What is CaSO4 (calcium sulphate ) also known as and what can it be used for?

A

-Gypsum
- Used for plastering

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16
Q

What catalyst would you use in a catalytic converter ?

A

Platinum (Pt) or Rhodium (Rh)

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17
Q

What is the equation for the chlorination of methane ( chlorine reacting with methane ) ?

A

CH4 + Cl2 => CH3Cl + HCl

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18
Q

What is the initiation step of the chlorination of methane ?

A

Cl2 => 2Cl•

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19
Q

What are the propagation steps for the chlorination of methane ?

Study These Flashcards
A

Cl• + CH4 => •CH3 + HCl
•CH3 + Cl2 => CH3Cl + Cl•

20
Q

What is the termination step for the chlorination of methane ?

Study These Flashcards
A

either
•CH3 + •CH3 => C2H6
•CH3 + Cl• => CH3Cl

21
Q

What is the general formula for a cycloalkane ?

22
Q

What are the dangers of producing carbon monoxide ( CO) ?

Study These Flashcards
A
  • Poisonous as it bonds to haemoglobin in the blood and prevents oxygen bonding.
23
Q

What is the danger of the production of soot ?

Study These Flashcards
A

global dimming and respiratory problems

24
Q

How do we get photochemical smog?

Study These Flashcards
A

When solid carbon particulates ( formed from incomplete combustion of hydrocarbons) and ozone mix together

25
EQ: State the meaning of fraction as used in the term petrol fraction (1)
A group of hydrocarbons with similar boiling points
26
Eq :what’s a catalyst for the cracking of head cane to form he cane and cyclopentane (1)
zeolite
27
EQ : give a reason why co2 absorbs infrared radiation (1)
C=O bonds vibrate at the same frequency as IR
28
EQ : suggest why chemists usually aim to design production methods with fewer steps with a high percentage atom economy (2)
Fewer steps : less energy used High percentage atom economy : less waste
29
EQ : how is fractional distillation used to separate octane (bp 125) and isooctane (bp 95) (2)
- isooctane has a lower boiling point so boils first - Isooctane condenses and is collected
30
what’s an equation to show how nitrogen monoxide is removed using catalytic converter
2CO + 2NO => 2CO2 + N2
31
what’s an equation to show formation of acid rain
S + O2 => SO2 ( acid rain ) CH3SH + 3O2 => SO2 + CO2 + 2H2O
32
what’s an equation to show removal of acid rain
SO2 + CaO => CaSO3
33
what’s an equation to show incomplete and complete combustion of nitrogen oxides
N2 + O2 => 2NO N2 + 2O2 => 2NO2
34
what are metals used inside catalytic converters
platinum palladium rhodium
35
EQ : platinum , palladium and rhodium are metals used inside catalytic converters . A very thin layer of the metals is used on a honeycomb ceramic support . Explain why a thin layer is used din this way (2)
- provides a larger surface area - Small amount of metal needed
36
what is a petroleum fraction
mixture of hydrocarbons with a similar chain length and boiling point range
37
what are the key points for fractional distillation industrially
- oil is preheated then passed into column - fractions condense at different heights - temp of column decreases upwards - separation depends on boiling point - boiling point depends on size of molecules - the larger the molecule the larger the VDW - similar molecules ( size , bp , mass ) condense together - small molecules condense at the top at lower temperatures - and big molecules condense at bottom at higher temps
38
what is a vacuum distillation unit and what does it allow
- heavy residues from the fractionating column are distilled again under a vacuum - lowering the pressure over a liquid will lower its boiling point - allows heavier fractions to be further separated without high temperature which could break them down
39
what is a free radical
a reactive species which possess an unpaired electron
40
what’s the conditions for thermal cracking
high pressure high temperature
41
what does thermal cracking produce
mostly alkenes sometimes produced hydrogen ( haber process)
42
what are the conditions for catalytic cracking
slight or moderate pressure high temperature
43
what do catalytic cracking usually produce
branched and cyclic alkenes and aromatic hydrocarbons
44
what’s catalytic cracking used for
to make motor fuels
45
why is catalytic cracking cheaper than thermal
it saves energy as lower temperature and pressures are used
46
what’s the dangers of nitrogen oxides
NO is toxic and can form acidic gas NO2 NO2 is toxic and acidic and it forms acid rain
47
EQ : what is meant by the term molecular formula
actual number of atoms of each element

Chemistry Year 12 (26 decks)

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