3Alkanes (2) 🫧 Flashcards
(11 cards)
What happens to the following when the alkane chain gets longer…
Flammability?
Boiling point?
Viscosity?
Hard to ignite
Bp increases
Low viscosity- doesn’t flow well
What happens in fractional distillation
- crude oil heated to 370 degrees. Column is hot at bottom, cold at top
- vapours pass up and condensate at the right temp and get piped off at their level
- larger chains are cracked producing smaller chains that are more useful
Explain thermal cracking
Temp is high 700-1200k and so is pressure 7000Pa
C-C bonds break forming 2 radicals that form a variety of shorter chains molecules
Lots of alkanes are produced
Explain catalytic cracking
Temp is 720k and pressure is just above atmospheric pressure and a zeolite catalyst is used
Makes branched alkanes, cycloalkanes and aromatic compounds
What are the products of complete combustion?
CO2
H2O
Lots of energy
What are the products of incomplete combustion?
CO
H2O
With even less oxygen,
Soot (C)
Often happens with long chains that need more oxygen to burn
Less energy is released
Why do branched molecules have lower bps?
They can’t pack as close together so the van der waals aren’t as effective
What is initiation?
The first one your reacting with the substance is split into radicals with uv
Eg.) Cl2 —> Cl* + Cl*
What is propagation?
- Use one of the radicals to react with the one your reacting it with in the question. The H goes with the halogen. The other product is a radical
Eg.) Cl* + CHF3 —> HCl + CF3* - Use this radical and ready it with the first reactant in the initiation- the halogen. You produce the same radical as in initiation.
Eg.) CF3* + Cl2 —> Cl* + CF3Cl
What is termination?
Reactions the two radicals that were not involved in the initiation step
Eg.) CF3* + CF3* —> C2F6
What’s the overall equation to represent the decomposition of ozone into oxygen?
2O3 —> 3O2
