C15 Flashcards
Ozone layer
- formed at outer edge of stratosphere
- 10km - 40km above Earths surface
- absorbs most of biologically damaging UV radiation (UV-B) from Suns rays
UV-B rad
dangers of uv-b
most linked radiation to sunburns
fears that increased UV-B can lead to increased genetic damage + skin cancer in humans
reaction of ozone in stratosphere
O2 -> 2O
steady state set up involving O2 and O radicals
O2 + O (equilibrium sign) O3
Human activity, especially use of CFCs has disrupted this equilibrium
CFCs main uses
refrigerants e.g. AC units and as aerosol propellants
Why are CFCs very stable
due to the high strength of C-F and C-Cl bonds in their molecules
What happens to CFCs at stratosphere?
UV radiation provides sufficient energy to break C-X bond in CFCs by homolytic fission forming radicals
C-Cl bond: lower bond enthalpy - so this bond breaks
What is the breakdown of CFCs called?
Photodissociation, because its breakdown is initiated by radiation
1987 Montreal Protocol
- introduced steps for complete removal of CFCs
- except for few products where no alternative could be found
- e.g. refrigeration / AC –> coolants using hydrocarbons, ammonia, carbon dioxide
Properties of CFCs
- Unreactive
- Inert - chemically stable in troposphere
- Non-Flammable
- Non-toxic
- Volatile
As a gas: easily compressed, low bp, liquefied under pressure
Nucleophile
Electron pair donor
Hydrolysis
Chemical reaction invoking water / aq solution of hydroxide - causes breaking of bond in a molecule
-results in molecule being split into 2 parts
How can haloalkanes be converted into alcohols?
using aqueous NaOH
reaction mixture heated under reflux
Hydrolysis and carbon halogen bond strength
Going down the group carbon halogen bond strength decreases
Weaker the carbon-halogen bond, the less energy needed to break this bond, so less time taken for reaction to reach completion
Measure rate of reaction of primary haloalkanes
Carry out reaction using silver nitrate:
Ag+ + X- –> precipitate of AgX
Water is present in aq silver nitrate
As haloalkanes are insoluble - carry out reaction in presence of ethanol solvent
Ethanol allows water and haloalkane to mix
