3Alkanes (2) 🫧

Question 1

What happens to the following when the alkane chain gets longer…
Flammability?
Boiling point?
Viscosity?

Answer 1

Hard to ignite
Bp increases
Low viscosity- doesn’t flow well

Question 2

What happens in fractional distillation

Answer 2

• 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

Question 3

Explain thermal cracking

Answer 3

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

Question 4

Explain catalytic cracking

Answer 4

Temp is 720k and pressure is just above atmospheric pressure and a zeolite catalyst is used
Makes branched alkanes, cycloalkanes and aromatic compounds

Question 5

What are the products of complete combustion?

Answer 5

CO2
H2O
Lots of energy

Question 6

What are the products of incomplete combustion?

Answer 6

CO
H2O

With even less oxygen,
Soot (C)

Often happens with long chains that need more oxygen to burn

Less energy is released

Question 7

Why do branched molecules have lower bps?

Answer 7

They can’t pack as close together so the van der waals aren’t as effective

Question 8

What is initiation?

Answer 8

The first one your reacting with the substance is split into radicals with uv
Eg.) Cl2 —> Cl* + Cl*

Question 9

What is propagation?

Answer 9

1. 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*
2. 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

Question 10

What is termination?

Answer 10

Reactions the two radicals that were not involved in the initiation step
Eg.) CF3* + CF3* —> C2F6

Question 11

What’s the overall equation to represent the decomposition of ozone into oxygen?

Answer 11

2O3 —> 3O2