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Wjec Chemistry Unit 2 > 2.5 > Flashcards

2.5 Flashcards

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1
Q

What is a fossil fuel

A

Fossil fuel is one that is
derived from organisms that
lived long ago.

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2
Q

Advantages of fossil fuels

A
  • variety available - each use can be matched to appropriate fuel
  • available at all times
  • widely available
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3
Q

Disadvantages of fossil fuels

A
  • non-renewable
  • produces CO2 on combustion - greenhouse gas
  • combustion of fossil fuels that contain sulfur and nitrogen leads to acid rain
  • carbon monoxide is formed during incomplete combustion
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4
Q

What is a non-renewable source

A

Cannot be reformed in a reasonable timescale

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5
Q

What is acid rain and its environmental effect

A

Rain with lower than expected pH
Combustion of fossil fuels that contain sulfur and nitrogen produce the dioxides which react with water to form sulfuric acid and nitric acid
Contains sulfuric acid and nitric acid
Damages buildings, vegetation and aquatic life
Health issues for people with breathing difficulties

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6
Q

Why are alkanes generally unreactive

A

Non-polar and dont contain multiple bonds

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7
Q

What is combustion

A

When alkanes burn and react with oxygen in exothermic reactions and are used as fuels

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8
Q

Complete combustion

A

Combustion that occurs with excess oxygen
Sufficient oxygen is present
Carbon dioxide and water are produced

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9
Q

Incomplete combustion

A

Combustion that occurs with insufficient oxygen
Carbon monoxide and water is formed
Less energy than complete combustion

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10
Q

Why is carbon monoxide toxic

A

Can inhibit transport of oxygen through the body as it combines with haemoglobin

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11
Q

What is halogenation

A

Reaction between organic compound and any halogen

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12
Q

What are the two important reactions of alkanes

A

Combustion and halogenation

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13
Q

What are the 3 mechanisms of halogenation

A

Initiation
Propagation
Termination

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14
Q

What is initiation in halogenation

A

Reaction that starts the process
Homolytic bond fission of chlorine to produce 2Cl•
Energy needed to break the bond is provided bu uv light

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15
Q

What is propagation in halogenation

A

Reaction by which the process continues/grows
Radicals take part as they’re so reactive
Starts with a radical then produces one so that the chain reaction occurs

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16
Q

Cl• + CH4 —>

A

CH3• + HCl

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17
Q

CH3• + Cl2 —>

A

CH3Cl + Cl•

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18
Q

What is termination in halogenation

A

The reaction that ends the process
Chain reaction continues until 2 radicals meet
CH3•+Cl• —> CH3Cl

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19
Q

Overall equation of halogenation

A

C2H6 +Cl2 —> C2H5Cl + HCl

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20
Q

What is a pi bond

A

One formed by the sideways overlap of p electrons
Double bond
High electron density above and below the plane of the molecule

21
Q

What makes alkenes susceptible to attach by an electrophile

A

The pair of electrons in the pi orbital

22
Q

What kind of bond fission is involved in electrophilic addition

A

Heterolytic

23
Q

What is an addition reaction

A

Reaction in which reagents combine to give one product

24
Q

What is shown by the curly arrows of this electrophilic addition

A

Movement of the electron pair

25
Q

If the attacking species is non-polar during electrophilic addition, how is a dipole induced

A

By the negative charge of the pi bond

26
Q

Test for alkenes

A

Reaction with bromine
• brown colour of bromine changes to colourless
• use of aqueous bromine as it is safer
Reaction with potassium manganate (VII)
Reaction with acidified potassium manganate
• purple manganate(VII) is decolorised

27
Q

Why, on the addition of HBr to alkenes , 2-bromopropane is the major product and not 1-bromopropane

A

It has greater stability of the 2• carbonation compared with the 1• carbonation

28
Q

Which type of carbocation

A

2•

29
Q

Which type of carbocation

A

1•

30
Q

What is polymerisation

A

Joining of a very large number of monomer molecules to make a large polymer molecule

31
Q

What is a monomer

A

Small molecule that can be made into a polymer

32
Q

What is a polymer

A

Large molecules made by joining many monomers

33
Q

What kind of molecules undergo addition polymerisation and why

A

Alkenes and substituted alkenes

They have a double bond which is used to join the monomers and nothing is eliminated

34
Q

Think of the polymer that would come of this monomer

A
35
Q

What is the name of the polymer of ethene

A

Poly(ethene)

36
Q

Properties of poly(ethene)

A

Unreactive and flexible

Can be used to make plastic bags

37
Q

Why do polymers have a huge variety of uses

A

The properties of polymers can be altered by using substituted alkenes as the monomer

38
Q

Properties of poly(propene)

A

Rigid

Used in food containers and kitchen equipment

39
Q

Properties of poly(chloroethene) or PVC

A

Flexible

Water pipes, waterproof clothes and insulating covering for electrical cables

40
Q

Properties of poly(phenylethene) or polystyrene

A

Hard - gives strength and rigidity

Made into an insulator by making holes in the structure

41
Q

Which polymer

A

Poly(propene)

42
Q

Which polymer

A

Poly(chloroethene)

43
Q

Which polymer

A

Poly(phenylethene)

44
Q

Why is CO2 bad for the environment

A

Absorbs infrared radiation from earth, then it emits it in all directions
Some of the radiation goes back towards the earth’s surface
Causes the surface’s temperature to rise
Can lead to rising sea levels and changes to crop stability

45
Q

Why are radical reactions hard to control

A

Further substitution can occur
A mixture of products may be formed
Unsatisfactory method of getting a high yield of a specific halogenoalkane
Can be largely avoided by limiting the amount if the halogen

46
Q

Name of this reaction

A

Electrophilic addition

47
Q

Monomer or repeating unit

A

Monomer

48
Q

Monomer or repeating unit

A

Repeating unit

Wjec Chemistry Unit 2 (8 decks)

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