4.1.2. Alkanes

Question 1

Formation of a sigma bond in alkanes

Answer 1

One sp3 orbital from each carbon overlap to form a single C-C bond called a sigma bond

Question 2

Boiling points

Answer 2

Increasing boiling points of alkanes can be explained by increasing number of electrons in the bigger molecules

Increases size of induced dipole-dipole interactions between molecules

Longer straight chains have a larger surface area of contact between molecules for London forces to form so have strong induced dipole interactions and higher boiling points

Question 3

Reactivity

Answer 3

Low reactivity of alkanes with many reagents

Due to high bond enthalpies of c-c and c-h bonds

Low polarity of sigma bonds

Question 4

cracking

Answer 4

Conversion of large hydrocarbons to smaller molecules by breaking c-c bonds

Question 5

Reasons for cracking

Answer 5

Petroleum fractions with shorter c chains are in more demand than larger fractions

To make use of excess larger hydrocarbons to supply demand for shorter ones

Products of cracking more valuable than starting materials

Question 6

Catalytic cracking

Answer 6

Slight pressure

High temperature (450C)

Zeolite catalyst

used for making motor fuels

Question 7

reaction of alkanes with bromine/cl2

Answer 7

UV light

homolytic fission - each atom gets one electron from the covalent bond

Question 8

free radical

Answer 8

reactive species which possess an unpaired electron