12 - Alkanes Flashcards
1
Q
What effect boiling point of alkanes
A
- chain length
- branching
2
Q
How does chain length effect bp
A
- LF act between mols which are in close surface contact
- as chain length increases, molecules have a larger surface area, so more surface contact is possible between molecules
- LF between mols is greater and so a larger amount of energy is required to overcome, resulting in larger bp.
3
Q
How else does chain length increase bp
A
- larger chain length means more atoms
- larger molar mass and more electrons
- we know the more electrons, greater the LF
- becomes stronger and so with more LF and intermolecular, more energy required to overcome resulting in higher bp
4
Q
How are alkanes used in everyday life
A
- gas and domestic fuel
- petrol
- kerosene
- diesel
5
Q
Why are alkanes unreactive
A
- C-C and C-H (sigma bonds) are very strong
- C-C are non polar
- the electro negativity are similar so C-H are considered non-polar
6
Q
How does initiation start
A
The energy for this homolytic bond fission is provided by UV radiation
7
Q
Why is initiation important
A
- causes radicals to be formed which are highly reactive and able to react
8
Q
What is the first step of propagation known as
A
Known as abstraction - when the halogen takes the H to form H-Br
E.g Br abstracts H
9
Q
Why does termination take place
A
When the concentration of reactants lessen (get used up) or no radicals left for reaction to cycle
10
Q
Limitations of radical substitution
A
- may react differently or with the products (CH3Br or HBr) because they are so high in concentration and accumulated
- this can continue until all hydrogen atoms have been substituted
- substitution can occur in different parts of the chain
