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Chemistry > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

Alkanes:

What are Alkanes?

A

Saturared HC

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2
Q

Alkanes: Boiling Point & Chain Length

What happens to the Bp as the chain length increases?

A

Increases
↳ increase in electrons : more LFs

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3
Q

Alkanes: Boiling Point & Branches

Do long-chain Alkanes have a higher Bp than branched ones?

A

Yes
↳ branched = more compact : easier to break
↳ decrease in intermolecular forces

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4
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

What is needed for Alkanes to react w Halogens?

A

Sunlight (UV)

(3 step reaction)

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5
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

Cl is broken into free Radicals in presence of UV radiation

(Step 1: Initiation)

A
  • UV provides enough energy to break Cl-Cl bond (Photdissociation)
  • Bonds break evenly, each atom keeps an electron (Homolytic Fission)
  • Atom becomes a very reactive radical
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6
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

Cl free Radicals attack Methane breaking the C-H bond

(Step 2: Propagation (1))

A
  • Cl attacks Methane mol
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7
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

Methyl free Radicals attack Cl mol

(Step 3: Propagation (2))

A
  • Methyl radical attacks Cl mol
  • New Cl radical can attack another methane mol
    ↳ until all Cl & CH4 mol are wiped out
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8
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

When 2 Radicals combine, a single mol is formed & chain reaction stops

(Step 4: Termination)

A
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9
Q

Alkanes: Reaction w Halogens/ Free Radical Subsitution Reaction

What’s the Problem with this reaction?

A

You end up with a mixture of products

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10
Q

Alkanes: Crude Oil

What is Petroleum?

A

Crude oil

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11
Q

Alkanes: Crude Oil

What is Crude Oil made of?

A

Mixture of HC
* Mainly alkanes

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12
Q

Alkanes: Crude Oil

What is Fractional Distillation?

A

Breaking longer alkanes into smaller ones

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13
Q

Alkanes: Crude Oil

Why do we use Fractional Distillation?

A

Crude Oil isnt useful : so its separated into smaller units

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14
Q

Alkanes: Crude Oil

What happens as Crude Oil Vapour goes up the Fractionating Columns?

A

It cools down

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15
Q

Alkanes: Crude Oil

What happened to the Bp as you go down the Fractionating Columns?

A

It decreases
↳ longer alkanes are at the bottom

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16
Q

Alkanes: Crude Oil

What happens to HC with the lowest Bp?

A

They’re drawn off as gases at the top of the column
↳ they don’t condense

17
Q

Alkanes: Cracking havier fractions into smaller ones

What is Cracking?

A

Breaking long-chained alkanes into smaller HC

18
Q

Alkanes: Cracking havier fractions into smaller ones

Why do we use Cracking?

A

Smaller fractions are in high demand
↳ they’re more useful : valuable

19
Q

Alkanes: Cracking havier fractions into smaller ones

Example of Cracking

Alkane (long) → Alkane (smaller) + Alkene

A
20
Q

Alkanes: Types of Cracking

What is Thermal Cracking?

(heat)

A

Cracking using high temps & pressure

21
Q

Alkanes: Types of Cracking

What is Produced in Thermal Cracking?

A

Lots of alkenes

22
Q

Alkanes: Types of Cracking

What type of Alkanes is Thermal Cracking used for?

( 10 Carbons & above )

A

Longer
↳ have a high Bp

23
Q

Alkanes: Types of Cracking

What is Catalytic Cracking?

(catalyst)

A

Cracking using Zeolite Catalyst at moderate temps & pressure

24
Q

Alkanes: Types of Cracking

What is Produced in Catalytic Cracking?

A
  • Aromatic HC
  • Motor Fuels
25
Q

Alkanes: Types of Cracking

What type of Alkanes is Catalytic Cracking used for?

( 10 Carbons & below )

A

Smaller
↳ broken quicker

26
Q

Alkanes: Alkanes are reformed into Cycloalkanes & Aromatic HC

What is Knocking?

A

When Alkanes explode by themselves when the fuel is compressed in the engine

27
Q

Alkanes: Alkanes are reformed into Cycloalkanes & Aromatic HC

Which HC are most likely to cause Knocking?

A

Straight chained Alkanes

28
Q

Alkanes: Alkanes are reformed into Cycloalkanes & Aromatic HC

How could you decerease the likelyhood of Knocking?

A

Adding a branched chain & Cyclic HC to the petrol mixture
↳ combustion becomes more efficient

29
Q

Alkanes: Alkanes are reformed into Cycloalkanes & Aromatic HC

What is needed for Reforming to occur?

A

A catalyst

Chemistry (13 decks)

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