Chapter 12 Alkanes

Question 1

What are alkanes

Answer 1

the main parts of crude oil and natural gas.
Used as fuels.
Cn H2n+2

Question 2

The bonding in alkanes

Answer 2

each carbon atom is joined to four hydrogens by single covalent sigma bonds.
Sigma bonds form by the orbitals overlapping.

Question 3

The shape of alkanes

Answer 3

Each carbon atom is surrounded by 4 electron pairs in 4 sigma bonds, causing tetrahedral arrangement 109.5’
They can rotate freely around the sigma bonds.

Question 4

effect of chain length on boiling point

Answer 4

when it is longer there are a greater number of induced dipole forces. The london forces are greater to overcome the forces.

Question 5

Effect of branching on boiling point

Answer 5

If there is branching then there are fewer surface points of contact which means there will be fewer london forces. The branches prevent the molecules from getting close together as straight- chain molecules.

Question 6

Combustion of Alkanes

Answer 6

CxHy + (x + y/4 )O2 + y/2 H2O

Question 7

Reaction of alkanes with halogens

Answer 7

IN presents of UV radiations alkanes react with halogens. This involves radical substitution.
Explain the Intiation step , two propagation steps, 3 termination steps

Question 8

Limitations of radical substitution in organic synthesis

Answer 8

There may be multiple molecules which continue on the cycle and there may be further substitutions of the hydrogen to the halogens.
There may be substitution at different positions in a carbon chain.