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Chem Miss D > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

How does the boiling point change as number of carbon increases?

A

Increases

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2
Q

Straight chain alkanes boiling point?

A

Higher than alkanes with same number of carbons but have branches

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3
Q

Single branch alkanes boiling point

A

Lower boiling point then straight chain alkanes with same number of carbons but higher than double branch alkanes with same number of carbons

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4
Q

Double branch alkanes boiling point

A

Lower boiling point than single and straight chain alkanes with same number of carbon

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5
Q

Forces in chemistry in nature are?

A

Electrostatic

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6
Q

Large intermolecular forces?

A

Higher boiling point

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7
Q

What type of intermolecular bonding is used for weak intermolecular forces?

A

Van Dee Waals

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8
Q

What is Van Der Waals bonding caused by?

A

Electrons creating instantaneous dipole (induced dipole forces)

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9
Q

Instantaneous polarity definition

A

A shift n the centre of gravity to a negative charge cloud with respect to the positive charge cloud

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10
Q

Where does instantaneous polarity occur?

A

In all atoms

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11
Q

Positive nucleus

A

Has a positive charge cloud

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12
Q

Negative outside

A

Negative charge cloud

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13
Q

What happens to Van der Waals bonding when when there are more electrons and longer chain?

A

Van der Waals bonding increases

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14
Q

When is Van Der Waals bonding the highest?

A

-when molecules have a lot of surface contact

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15
Q

How can straight chain molecules have more surface contact?

A

The pack closer

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16
Q

What do branches alkanes commonly make?

A

Petrol

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17
Q

What does using greater branching alkanes do to petrol?

A
  • decreases boiling point

- makes combustion process in engine more efficient

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18
Q

How many molecules have Van Der Waals bonding?

A

All of them

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19
Q

Electro negativity definition

A

The measure of an atoms ability to pull shared electrons to itself

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20
Q

What elements are used for Dipole/dipole bonding and hydrogen bonding?

A
  • Nitrogen
  • Oxygen
  • Flurione
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21
Q

Order in weakest to strongest types of intermolecular bonding

A
  • Van Der Waals
  • Dipole/dipole
  • Hydrogen
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22
Q

What type of polarisation in Dipole/dipole bonding?

A

Permanent polarisation

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23
Q

Requirements for hydrogen bonding

A

1) Hydrogen atom attached to either N O or F

2) Neighbouring molecule with highly electric negative atom (NOF) with a lone pair of electrons

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24
Q

Fluorine and hydrogen bond

A
  • Fluorine pulls election from hydrogen as bonding is so strong and forms covalent bond
  • Hydrogen bond formed (dative bond) where both electrons come from the same atom
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25
Q

Alkanes general formula

A

CnH2n+2

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26
Q

Source of alkanes

A

Crude oil

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27
Q

High viscosity definition

A

Thicker

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28
Q

Low viscosity definition

A

More runny

29
Q

What type of bonding to alkanes have?

A

Van Der Waals

30
Q

Fractional distillation steps

A
  • plankton died at bottom of sea and form fossils which make crude oil
  • crude oil vaporised
  • vapour passed into to column which is hot at bottom and cool at top
  • vapour rises and cools
  • molecules condense at different point as have different boiling points
  • larger molecule (higher bp) lower down column condenses
31
Q

Cracking definition

A

Breaking carbon-carbon bonds

32
Q

2 types of cracking

A
  • Thermal

- catalytic

33
Q

What does catalytic cracking give a high proportion of?

A

Cyclo alkanes

34
Q

What does cracking produce some of?

A

Unsaturated alkanes

35
Q

Alkanes definition

A

A homologous series of saturated hydrocarbons

36
Q

Can alkanes react?

A

They are unreactive but do burn and react with halogens (chlorine)

37
Q

gases produced from crude oil from lowest to highest boiling points

A
  • fuel gases
  • gasoline
  • naphtha
  • kerosene
  • diesel
  • residue
38
Q

Why are shorter chain alkanes in higher demand?

A

-more useful as are more flammable and burn with cleaner flame

39
Q

Cracking definition

A

-thermal decomposition of alkanes

40
Q

What does cracking produce?

A

Shorter c chain alkanes

41
Q

Reforming definition

A

Straight chain carbons are converted to branches chain alkanes and cyclic alkanes (both burn more efficiently)

42
Q

Why are alkanes good as fuels?

A

Readily burn in presence of oxygen (highly exothermic)

43
Q

Complete combustion equation produces?

A

CO2 + H2O

44
Q

Incomplete combustion equation produces?

A

CO + H2O
Or
C + H2O

45
Q

How is acid rain formed?

A

Sulfur containing impurities are found in petroleum fractions which produce SO2 when they are burned which leads to acid rain

46
Q

Homolytic fission definition

A

The Cl - Cl bongos broken by uv radiation (catalyst) by homolytic fission

47
Q

What is homolytic classed as ?

A

A chain reaction

48
Q

Free radical definition

A

An atom either by itself or part of a molecules that had a free electron ready to form a covalent bond

49
Q

Propagation definition

A

Continuing the reaction

50
Q

When does propagation occur?

A

When further reaction produces more free radical

51
Q

Initiation definition

A

Start of reaction

52
Q

Termination definition

A

End of reaction

53
Q

Diatomic definition

A

2 of molecule

54
Q

Instantaneous dipole definition

A

The separation of charges in a non-polar molecule at an instant due to sudden disturbance in the electric cloud around the molecule results in an instantaneous dipole.

55
Q

Free radical substitution for CH4 + Cl2 -> CH3Cl + HCl

A 
Initiation
Cl - Cl -> 2.Cl
Propagation
CH4 + .Cl -> HCl + .CH3
.CH3 + Cl2 -> CH3Cl + .Cl
Termination 
.Cl + .Cl -> Cl2
.CH3 + .CH3 -> C2H6
.CH3 + .Cl -> CH3Cl
56
Q

Why do we use HFCs instead of CFCs?

A

Because the ozone layer was attacked by CFCs and thinned down so now we use HFCs

57
Q

Ozone layer main equation

A

O2 -> (UV) O. + O.

O2 + O. -> O3

58
Q

What conditions does thermal cracking take place?

A
  • high temp up to 1000 degrees

- high pressure

59
Q

What does thermal cracking produce?

A

Lots of alkanes

60
Q

Catalytic cracking conditions

A
  • slight pressure

- high temp (about 500 degrees)

61
Q

What does catalytic cracking mostly produce?

A
  • aromatic hydrocarbons

- alkanes needed to produce motor fuels

62
Q

How does using a catalyst cut costs?

A

Reaction can done at low pressure and a lower temp and speeds up reaction so saves time and money

63
Q

How is nitrogen monoxide produced?

A

When high pressure and temperature in car engine causes the nitrogen and oxygen atoms from the air to react together

64
Q

What do nitrogen oxides reacting with sunlight produce?

A

Ground level ozone

65
Q

What happens if sulfur dioxide or nitrogen dioxide gets into the atmosphere?

A

Dissolves on the moisture and is converted into sulfuric acid or nitric acid

66
Q

What is the greenhouse effect?

A

When greenhouse gases absorb infrared energy (heat) they emit some of the energy they absorb back toward the earth keeping it warm

67
Q

Global warming definition

A

More carbon dioxide in the atmosphere making the earth warmer

68
Q

What does CFC stand for?

A

Chloroflurocarbon

Chem Miss D (8 decks)

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