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Chemistry > Organic (3.3) > Flashcards

Organic (3.3) Flashcards

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1
Q

Why is cracking used?

A

-Low demand but high supply of long-chain hydrocarbons
-High demand but low supply of shorter-chain (especially naptha fraction)
Alkenes produced are much more reactive than naturally occurring alkanes, so better used as fuels

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2
Q

What is cracking?

A

Splitting up of longer-chain hydrocarbons to produce shorter chain hydrocarbons

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3
Q

What conditions are required for thermal cracking?

A
  • 700-1200K

- 7000kPa

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4
Q

What are the products of thermal cracking?

A
  • Alkanes & Alkenes (1:1)

- Formed through intermediate, highly reactive free radicals

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5
Q

What conditions are required for catalytic cracking?

A
  • 720K
  • Slight pressure
  • Zeolite catalyst (honeycomb structure, aluminium oxide & silicon dioxide)
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6
Q

What are the products of catalytic cracking?

How are they separated?

A
  • Branched alkanes
  • Cycloalkanes
  • Aromatic compounds

-Separated by fractional distillation

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7
Q

Describe features of fractional distillation

A
  • Continuous process
  • Large scale
  • Multiple collection points
  • Produces fractions (mixtures of similar bpts)
  • Used to separate complex mixtures with close bpts)
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8
Q

Describe the features of simple distillation

A
  • Batch process
  • Small scale
  • Single collection point
  • Produces pure substances (single bpt)
  • Used to separate simple mixtures with widely different bpts
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9
Q

What is isomerism?

A

Molecules with the same molecular formula, whose atoms are arranged differently

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10
Q

What is structural isomerism?

A

Molecules with the same molecular formula, with differing structural formulae

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11
Q

What is position isomerism?

A

(STRUCTURAL)

-The functional groups are the same but attached to the chain at differing points

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12
Q

What is functional group isomerism?

A

(STRUCTURAL)

-Same molecular formula but different functional groups

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13
Q

What is chain isomerism?

A

(STRUCTURAL)

  • Same molecular formula but the chain is arranged differently
  • (e.g. branching etc)
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14
Q

What is stereoisomerism?

A

Molecules have the same structural formula, but are arranged differently in space

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15
Q

What is geometric isomerism?

A

(STEREO)

  • E-Z isomerism refers to the orientation of the largest molecules around a double bond
  • E=different side
  • Z=same side
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16
Q

How does geometric isomerism arise?

A

It arises due to restricted rotation about a double bond

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17
Q

What is optical isomerism?

A

(STEREO)

  • Occurs when four different substituents are attached to one carbon atom (chiral carbon)
  • Essentially a reflection (cannot be superimposed)
18
Q

What is a racemic mixture?

A
  • A racemic mixture is a 50:50 mix of two enantiomers

- Optically inactive as the enantiomers rotate the plane of polarization of polarised light oppositely

19
Q

Why are racemic mixtures formed?

A

Racemic mixtures are formed as the likelihood of attack from above or below the planar centre is equal, creating two opposing forms of chiral molecules

20
Q

What are the products of complete combustion?

A

-H2O & CO2

21
Q

Describe the enthalpies of combustion reactions

A
  • Combustion reactions give out large amounts of heat, and hence have large negative enthalpies
  • The more carbons present, the greater the heat output, and the larger the negative enthalpy (but the harder they are to ignite)
  • Heavily exothermic
22
Q

What is a fuel?

A
  • A substance that releases heat energy when it undergoes combustion
  • One which stores a large amount of energy for a small weight
23
Q

What is incomplete combustion?

A

-A combustion reaction that takes place in a limited supply of oxygen (not lack of)

24
Q

What are the products of incomplete combustion?

A
  • CO & H2O

- In even less oxygen: C (soot) & H2O

25
Q

Why is incomplete combustion dangerous?

A
  • The release of CO is dangerous as it is toxic. It binds to the haemoglobin in the blood in place of oxygen, preventing transportation around the body. Leads to death by asphyxiation.
  • CO is also odourless and colourless so is hard to detect
26
Q

What is the danger of reactions between nitrogen and oxygen in internal combustion engines?

A
  • Nitrogen oxides, NOx (NO, NO2, N2O4) are produced at high temperatures
  • These oxides are dangerous as they can react with water vapour and oxygen in the air to form nitric acid
  • This nitric acid contributes to acid rain and photochemical smog
27
Q

What is the danger caused by sulfur-containing impurities in crude oil?

A
  • They produce sulfur dioxide which can combine with water vapour and oxygen in the air to create sulfuric acid
  • This is another contributor to acid rain
28
Q

What is the danger of the production of carbon particles?

A

-Carbon ‘particulates’ can exacerbate asthma and cause cancer

29
Q

What is the effect of unburnt hydrocarbons on the atmosphere?

A
  • They are significant greenhouse gases

- They contribute to photochemical smog (which has serious health affects)

30
Q

What is the effect of CO2 on the atmosphere?

A
  • Carbon dioxide is a greenhouse gas

- Its levels are rising worryingly as it is always produced when hydrocarbons burn

31
Q

What is the effect of water vapour on the atmosphere?

A

It is a greenhouse gas

32
Q

Why is flue gas desulfurisation done?

A
  • To remove sulfur dioxide given off by burning fossil fuels at power stations
  • Sulfur dioxide combines with oxygen and water in the atmosphere to form sulfuric acid which contributes to acid rain
33
Q

How do greenhouse gases warm the earth?

A

They trap infrared radiation from the sun so that it heats up the Earth’s atmosphere?

34
Q

What are the greenhouse gases?

A

Carbon dioxide (CO2), water vapour (H2O) & methane (CH4)

35
Q

Why are greenhouse gases important?

A

Without greenhouse gases, the Earth would be too cold to sustain life

36
Q

Why has level of CO2 increased?

A
  • Since the industrial revolution, fossil fuels have been used to fuel industrial plants
  • This releases CO2
37
Q

What is he role of water vapour in global warming?

A
  • Water vapour is the most abundant of the greenhouse gases
  • Its levels have stayed roughly the same over the same (except locally) so has had little effect
  • Rising temperatures may increase water vapour however
38
Q

What are the steps of the greenhouse effect?

A
  • Visible radiation from sunlight penetrates the atmosphere and warms the Earth
  • Invisible infra-red radiation is emitted by the Earth and cools it down, but some of this is trapped by greenhouse gases which act as a blanket
39
Q 
An alkane containing 30 hydrogen atoms per molecule, its empirical formula is:
A - C6H15
B - C7H15
C - C14H30
D - C15H30
A

Answer: B (C7H15)

-Simplest ratio of C14H30 (C2 H2n+2)

40
Q

Which statement is correct about fractional distillation?
A - A zeolite catalyst is used
B - Each fraction contains a mixture of hydrocarbons
C - Gaseous fractions are formed by breaking covalent bonds
D - The fractioning column is hottest at the top

A

Answer: B

Chemistry (4 decks)

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