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Chem Miss D > Alkanes > Flashcards

Alkanes Flashcards

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
Alkanes general formula
CnH2n+2
26
Source of alkanes
Crude oil
27
High viscosity definition
Thicker
28
Low viscosity definition
More runny
29
What type of bonding to alkanes have?
Van Der Waals
30
Fractional distillation steps
- 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
Cracking definition
Breaking carbon-carbon bonds
32
2 types of cracking
- Thermal | - catalytic
33
What does catalytic cracking give a high proportion of?
Cyclo alkanes
34
What does cracking produce some of?
Unsaturated alkanes
35
Alkanes definition
A homologous series of saturated hydrocarbons
36
Can alkanes react?
They are unreactive but do burn and react with halogens (chlorine)
37
gases produced from crude oil from lowest to highest boiling points
- fuel gases - gasoline - naphtha - kerosene - diesel - residue
38
Why are shorter chain alkanes in higher demand?
-more useful as are more flammable and burn with cleaner flame
39
Cracking definition
-thermal decomposition of alkanes
40
What does cracking produce?
Shorter c chain alkanes
41
Reforming definition
Straight chain carbons are converted to branches chain alkanes and cyclic alkanes (both burn more efficiently)
42
Why are alkanes good as fuels?
Readily burn in presence of oxygen (highly exothermic)
43
Complete combustion equation produces?
CO2 + H2O
44
Incomplete combustion equation produces?
CO + H2O Or C + H2O
45
How is acid rain formed?
Sulfur containing impurities are found in petroleum fractions which produce SO2 when they are burned which leads to acid rain
46
Homolytic fission definition
The Cl - Cl bongos broken by uv radiation (catalyst) by homolytic fission
47
What is homolytic classed as ?
A chain reaction
48
Free radical definition
An atom either by itself or part of a molecules that had a free electron ready to form a covalent bond
49
Propagation definition
Continuing the reaction
50
When does propagation occur?
When further reaction produces more free radical
51
Initiation definition
Start of reaction
52
Termination definition
End of reaction
53
Diatomic definition
2 of molecule
54
Instantaneous dipole definition
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
Free radical substitution for CH4 + Cl2 -> CH3Cl + HCl
``` 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
Why do we use HFCs instead of CFCs?
Because the ozone layer was attacked by CFCs and thinned down so now we use HFCs
57
Ozone layer main equation
O2 -> (UV) O. + O. | O2 + O. -> O3
58
What conditions does thermal cracking take place?
- high temp up to 1000 degrees | - high pressure
59
What does thermal cracking produce?
Lots of alkanes
60
Catalytic cracking conditions
- slight pressure | - high temp (about 500 degrees)
61
What does catalytic cracking mostly produce?
- aromatic hydrocarbons | - alkanes needed to produce motor fuels
62
How does using a catalyst cut costs?
Reaction can done at low pressure and a lower temp and speeds up reaction so saves time and money
63
How is nitrogen monoxide produced?
When high pressure and temperature in car engine causes the nitrogen and oxygen atoms from the air to react together
64
What do nitrogen oxides reacting with sunlight produce?
Ground level ozone
65
What happens if sulfur dioxide or nitrogen dioxide gets into the atmosphere?
Dissolves on the moisture and is converted into sulfuric acid or nitric acid
66
What is the greenhouse effect?
When greenhouse gases absorb infrared energy (heat) they emit some of the energy they absorb back toward the earth keeping it warm
67
Global warming definition
More carbon dioxide in the atmosphere making the earth warmer
68
What does CFC stand for?
Chloroflurocarbon

Chem Miss D (8 decks)

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