Alkanes

CO2 in atmosphere has
risen from 0.03% to 0.04%

Physical
Properties

boiling point of alkanes
increase with increasing
molecular mass

State at room
temperature -

C5-C7 = LIQUIDS

longer chain
alkanes = SOLIDS

shorter chain
alkanes = GASES

ISOMERS
with same RMM...

  • As RMM increases
  • VDW forces increase in strength
  • due to increasing no. of electrons

boiling point DECREASES
as amount of branching
INCREASES

molecules with branched chains have

  • FEWER points of contact
  • DECREASES strength of VDW forces
  • LOWERs b.pt.

Insoluble in water

Dissolve in non-polar liquids
like cyclohexane

Reactivity

generally
unreactive

DO undergo
combustion

COMBUSTION

Complete - produce
CO2 + Water

Incomplete - produce
CO, Water + soot (C)

dangers of CO

  • absorbs faster than O2
  • reacts with haemoglobin
    in RBC cells preventing
    carrying from O2

Petrol +
Diesel

primarily composed of a
blend of alkanes

exact nature
depends on
external conditions

winter - higher proportion of volatile,
short branched alkanes added to P/D
to help vehicles start

Pollution

Acid
Rain

BAD
REACTIONS

N2 + O2 -----> 2NO (nitrogen (II) oxide/monoxide)

N2 + 2O2 -----> 2NO2 (nitrogen (IV) oxide/ dioxide)

Rain that is more
acidic than normal

Fossil fuels normally contain
sulfur compounds

PROCESS

  1. SO2 + H2O -----> H2SO3
    (sulfurous acid/ sulfuric (IV) acid
  1. sulfurous acid oxidised to form
    sulfuric acid - H2SO4
  • defoliates + destroys trees + vegetation
  • corrodes buildings
  • kills fish

Photochemical
Smog

caused by
toxic gases

formed when:

  • nitrogen oxides
  • sulfur dioxides
  • unburned hydrocarbons
    react with SUNLIGHT
  • eye irritation
  • nasal congestion
  • respiratory problems
  1. When fossil fuels are burnt,
    sulfur dioxide is released
    S + O2 ----> SO2

Global
Warming

Greenhouse
Effect

2.Infrared radiation is radiated from
Earth towards space

  1. Gases (water vapour, methane + CO2)
    good at absorbing radiation + heating
    atmosphere up

1.electromagnetic radiation from
sun reaches Earth -

  • some reflected back into space
  • rest absorbed + heats up earth

D: describe the increasing average
temperature of Earth's surface

  • Increased dependency of
    fossil fuels for mankind =
  • rapid increase conc. CO2
    in atmosphere =
  • increase average surface temp

linked to climate
change around world

Catalytic
Converters

reduce the environmental
impact of exhaust systems
of petrol motor vehicles

converts pollutants
into less harmful
products

oxides of nitrogen reduced -> N + O
2NO ----> N2 + O2
2NO2 ----> N2 + 2O2

CO oxidised -> CO2
2CO + O2 ----> 2CO2

2 equations can be joined into 1
2NO + 2CO ----> N2 + 2CO2

Why work better
@ 150°C+?

  • higher temp
  • more collisions
  • works more effectively

honeycomb structure -

  • allows gas to pass through
  • large SA for reaction to take
    place

coated w/ layer of platinum & rhodium -

  • metal expensive
  • but thin coating keeps
    costs down

leaded petrol stop catalyst from
working as coats surface w lead,
rendering metal catalyst passive