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Chem 2: Developing Fuels > DF6: Alkenes and Addition Reactions > Flashcards

DF6: Alkenes and Addition Reactions Flashcards

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1
Q

What shape does a single carbon bond have?

A

Tetrahedral

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2
Q

What is the angle between two carbon atoms in a single covalent bond?

A

109.5 degrees

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3
Q

What shape does a carbon double bond have?

A

Trigonal Planar

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4
Q

What is the angle between two carbon atoms in a double bond?

A

120 degrees

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5
Q

Do all the carbon atoms in an alkene compound lie in a planar shape?

A

No only those in the double bond e.g ethene is completely planar but in propene only the C=C unit is

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6
Q

What type of bond is a single covalent bond?

A

A sigma bond

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7
Q

How is a sigma bond formed?

A

When two s orbitals overlap in the space between two atoms

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8
Q

Why are sigma bonds very strong?

A

There is the highest possible electron density between the two positive nucleui as the two s orbitals overlap

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9
Q

How is a pi bond formed?

A

When two p orbitals overlap sideways

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10
Q

What does a pi bond consist of?

A

2 areas of negative charge, one above and one below the line of atoms

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11
Q

What is a carbon - carbon double bond made up of?

A

One sigma bond and one pi bond

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12
Q

Why is a double bond not twice as strong as a single bond?

A

Because pi bonds are weaker than sigma bonds

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13
Q

Define an “electrophile”

A

A positive ion/molecule with a positive partial charge which accepts a lone pair of electrons to form a covalent bond

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14
Q

Define an “addition reaction”

A

Two or more molecules reacting to form a larger single molecule

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15
Q

Why does the carbon-carbon double bond have a highly negative region?

A

The four electrons in the double bond of ethene give the region between the two atoms a higher than normal negative charge density

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16
Q

What can be used as a test for the saturation of a hydrocarbon?

A

Shaking the compound with bromine water

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17
Q

What occurs with an alkene is shaken with bromine water?

A

It goes from orange to colourless

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18
Q

What occurs with an alkane is shaken with bromine water?

A

It stays orange

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19
Q

Write a formula for the electrophilic addition of bromine to an alkene

A

H2C=CH2 + Br2 ====> CH2BrCH2Br

20
Q

Describe the first step of electrophilic addition with bromine (polarisation)

A

The bromine molecule moves closer to the negative C=C bond which repels electrons to the bottom of the br-br bond, polarising the molecule and creating a postively charged (an electrophile) bromine atom

21
Q

Describe the second step of electrophilic addition with bromine (carbocation)

A

An electron pair from the C=C bond attacks the positive bromine atom, forming a dative covalent bond, the carbon atom the electron pair came from becomes a carbocation

22
Q

Describe the third step of electrophilic addition with bromine (new covalent bond)

A

A pair of electrons moves from the now negative bromide ion to the carbocation to form a new carbon-bromine covalent bond

23
Q

What product is formed from the electrophilic addition of ethene with bromine?

A

1,2-dibromoethane

24
Q

How does ethene react with hydrogen bromide solution and what is formed?

A

Readily at a room temperature in a polar solvent to form bromoethane

25
Q

What occurs if HBr is added to an unsymmetrical alkene?

A

Two products are formed e.g with propene: 2-bromopropane and 1-bromopropane is formed

26
Q

How do alkenes create alcohols?

A

By hydrating them in the presence of an acid catalyst

27
Q

Give the overall equation for the hydrolysis reaction of an alkene with water

A

H2C=CH2 + H20 ===H2SO4===> C2H5OH

28
Q

Give the steps of the hydrolysis reaction of alkene with water and their formulas (4)

A

1) Cold concentrated sulfuric acid reacts with an alkene in an electrophilic addition reaction
H2C=CH2 + H2SO4 ====> CH3CH2OSO2OH
(ethene) + (sulfuric acid) ====> (ethyl hydrogen sulfate)

2) Cold water is added and the product is warmed, it is hydrolysed to form an alcohol
CH3CH2OSO2OH + H2O ====> CH3CH2OH + H2SO4
(ethanol)

29
Q

How can ethene be turned into ethanol?

A

Through the process of steam hydration

30
Q

What temperature must the steam hydration of ethene occur at?

A

300 degrees c

31
Q

What pressure must the steam hydration of ethene occur at?

A

600atm

32
Q

What type of reaction is the steam hydration of ethene?

A

A reversible one

33
Q

Give the equation for the steam hydration of ethene

A

H2C=CH2 + H2O ⇌ C2H5OH

34
Q

What kind of catalyst is used during the steam hydration of ethene?

A

A solid phosphoric acid catalyst absorbed onto solid silica

35
Q

How low is the reaction yield of the steam hydration of ethene?

A

5%

36
Q

How can is the overall yield of the steam hydration of ethene increased from 5% to 95%?

A

By recycling unreacted ethene gas

37
Q

How does ethene form ethane?

A

By reacting with hydrogen gas

38
Q

Why is a catalyst needed in the hydrogenation of ethene?

A

To break the strong hydrogen - hydrogen bonds and form hydrogen atoms that can react with the alkane

39
Q

What are the two catalysts that can be used in the hydrogenation of ethene?

A
  • Platinum

- Nickel

40
Q

What is the advantage of using nickel over platinum as a catalyst?

A

It is cheaper

41
Q

What is the disadvantage of using nickel over platinum as a catalyst?

A

It is less efficient

42
Q

In what conditions is platinum used as a catalyst in the hydrogenation of ethene?

A

Standard laboratory conditions

43
Q

Under what temperature is nickel used as a catalyst in the hydrogenation of ethene

A

150 degrees c

44
Q

Under what pressure is nickel used as a catalyst in the hydrogenation of ethene?

A

5atm

45
Q

Give the formula for the reaction of ethene with hydrogen?

A

H2C=CH2 + H2 ====> CH3CH3

46
Q

Give one usage of hydrogenation

A

To make unsaturated fats and oils more saturated and therefore thicker

Chem 2: Developing Fuels (11 decks)

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