Hydrocarbons:

Fractional distillation of crude oil:

Video clip

  • The crude oil is vaporised before entering the column at 650K.
  • The column has a temperature gradient hot at the bottom getting gradually cooler as you go up the column.
  • The column is divided into trays, each tray has bubble caps for vapour to rise
  • As the hot vapour rises into a tray it comes in contact with cooler part of the column.
  • Eventually the hydrocarbon will reach a part of the column where its temperature is lower than its boiling point.  At this point it will condense in the tray.

  • The top of the column has the most volatile hydrocarbons, those with the lowest boiling points.

  • The bottom of the column has the least volatile hydrocarbons, those with the highest boiling points.

 

Boiling points of the alkanes:

Effect of branching:

Activity: 

        1)  Construct a molecule of pentane, how well do they line up against each other?

        2)  Repeat this for the 2 isomers.

Pentane

309K
2-methylbutane

301K
2,2-dimethylpropane

283K
  • Pentane can be described as sausage shape.  These can get close and have maximum surface area.

  • 2,2 dimethylpropane is spherical in shape.  It cant pack together quite as well and has a minimum surface area:

 

Questions 1-2  P119

 

Hydrocarbons as Fuels

The combustion of alkanes:

Practical

Video clip

CH4(g)      +             2O2(g)                     CO2(g)        +              2H2O(g)

Incomplete combustion:

CH4(g)      +          11/2O2(g)                   CO(g)          +              2H2O(g)

Cracking:

Practical

 

Video clip

  • Cracking breaks longer, less useful alkanes into shorter, more useful alkanes and alkenes.

  • This is done at heating the alkanes with a catalyst.

  • Both C C and C H bonds are broken in the process.  Random bonds are broken which means a variety of products are produced including hydrogen.  Some of the intermediates can react to produce branched chain alkanes.

  • Alkenes are used in the polymer industry.

  • One such reaction is:

Producing branched chains:

Producing cyclic hydrocarbons:

Improving fuels:

100% Burns efficiently
0% Burns inefficiently

Questions  1-4  P121

Questions  6-9  P143

 

Fossil fuels and fuels of the future

The crude oil economy:

The use of crude oil for fuels:

  Carbon monoxide - toxic gas
  Carbon dioxide - global warming
  Nitrogen oxides - acid rain / forest destruction
  Sulphur oxides - acid rain

The greenhouse effect - global warming:

  • Radiation from the sun reaches the planet.
  • The radiation is absorbed by the Earth and re emitted as IR radiation.
  • Most of this IR radiation goes back into space but some is absorbed by gases in the atmosphere.
  • These gas molecules absorb the IR radiation then re emit it as energy, this energy warms up the atmosphere.
  • These gases are:  water, methane and carbon dioxide.

How do gases absorb radiation?

  • Just like IR spectroscopy, the bonds in these greenhouse gases absorb IR radiation in their bonds.
  • The bonds vibrate absorbing the IR radiation.
  • Different gases will absorb different amounts of IR radiation.
  • 3 factors determine the impact a gas has on Global warming:
  1. Its concentration in the atmosphere
  2. Its ability to absorb IR radiation
  3. Its lifetime in the atmosphere
  • These 3 factors make up the GWP (Global Warming Potential)
  • The term Climate Change explains that although the average temperature of the planet is rising, different areas around the planet will suffer from extreme weather patterns.

Solutions to the Greenhouse Effect:

Carbon Capture and Storage, CCS:

  CH4(g) + 2O2(g) CO2(g) + 2H2O(g)        
  CH4(g) + 2H2O(g) CO2(g) + 4H2(g)        

Storage as carbonates:

  CaO(s) + CO2(g) CaCO3(s)            
  MgO(s) + CO2(g) MgCO3(s)            

Fuels of the future:

Questions P123  Qu 1 - 3

Substitution reactions of the alkanes

Halogenation of the alkanes:

             CH4(g)            +          Cl2(g)                          CH3Cl(g)        +          HCl(g)

C6H14(g)         +          Br2(g)                         C6H13Br(g)     +          HBr(g)

Mechanism for chlorination

The mechanism:

Step 1:  Initiation:

                   Cl2                  Cl.           +          Cl.           UV light

Step 2:  Propagation:

          

Step 3:  Termination:

                   Cl.        +       Cl.                   Cl2

                   .CH3    +       .CH3               CH3 CH3

                   Cl.        +       .CH3               CH3Cl

 Overall

                   CH4     +       Cl2                  CH3Cl    +    HCl

Further reactions of chloromethane:

Summary of photochemical reaction:

initiation

                   Cl2                  Cl.           +          Cl.           UV light

Propagation

           

Termination

                   Cl.        +       Cl.                   Cl2

                   CH3.    +       CH3.               CH3 CH3

                   Cl.        +       CH3.               CH3Cl

Overall

                   CH4     +       Cl2                  CH3Cl    +    HCl

Further substitution               CH2Cl2, CHCl3, CCl4

Revision:  The alkanes:

Questions  P125  Qu  1-2

Alkenes

The reactivity of the C=C double bond:

Physical properties of the alkenes

Introduction:

The nature of the double bond:

Cyclic alkenes:

  • Cyclic means that the carbon chain is joined at either end forming a ring.
  • The reactions of cyclic alkenes is exactly the same as straight chain alkenes
  • As there is no 'ends' to the molecule they have 2 H's less in the general formula.
  • Carotene (below) has cyclic and straight chain double bonds (11)

 

Practical

Questions  P127  1-4

Reactions of alkenes:

The reactivity of the C=C double bond:

Bond Bond enthalpy Kj mol-1
C-C +347
C=C +265

Reactions of the alkanes:

Practical    note:  leave an alkane with bromine water in the window for the rest of the lesson, discuss this observation.

1)    Addition of hydrogen:

2)    Addition of halogens:

The mechanism:

3)    Addition of hydrogen halides:

Mechanism:

            Definition - Carbocation is an organic ion in which a carbon atom has a positive charge

Addition to unsymmetrical alkenes:

.

        You will be expected to identify both products.  You will not need to identify the major / minor products

4)    Addition of steam:

Alkenes with more than one double bond:

Revision:  the chemistry of the alkenes

Questions  P129  Qu 1-2  /  P131 Qu 1-2  /  P133  Qu 1-3  /  P143  Qu 10 - 12, 14

Industrial importance of alkenes:

Unsaturated compounds in industry:

Making polymers

                   nCH2 = CH2                             -[  CH2 CH2 ]-n

                   monomer                                      polymer

Practical

Polymers and industry:

1)    Radical polymerisation:

2)    Ziegler Natta process:

Questions  P135  Qu 1-3

 

Polymer chemistry:

 

Addition polymerisation:

Some common polymers:

 

 

 

 

 

Identifying the monomer:

Questions  P137  Qu 1-2

Polymers - dealing with our waste:

Recycling

Burning

Feedstock recycling

Read P138 - 141, answer questions 1-4 P139  /  1  P141

Revision:

Questions  13, 15  P 143  /  1-6  P 144,145