Alkanes

Question 1

What bonds are formed in Alkanes?

Answer 1

Sigma bonds

Question 2

What is a homologous series?

Answer 2

Group of organic compounds that have the same general formula and same functional group where each member differs by CH2

Question 3

What does branching do to the boiling point of alkenes and explain why

Answer 3

Branching decreases the boiling point
Straight chains without branches contain a larger surface area meaning they have stronger Van Der Waals
Branched chains have a lower surface area resulting in weaker van Der Waals and a lower boiling point

Question 4

What is a aliphatic molecule?

Answer 4

Open chained, not rings

Question 5

What is a free radical?

Answer 5

A species with an unpaired electron

Question 6

What is a branched molecule?

Answer 6

Contains another group on the hydrocarbon

Question 7

How do sigma bonds form?

Answer 7

The end on end overlap of s or p orbitals

Question 8

What is always formed when an Alkane is burnt in an excess of O2?

Answer 8

CO2 and H2O

Question 9

What do sigma bonds allow?

Answer 9

Free rotation

Question 10

Explain the boiling points of long Alkane chains compared to short ones

Answer 10

Longer Alkane chains have a higher boiling point. Alkanes are non polar. They have van der waals forces so the increase in boiling point is due to stronger Van Der Waals forces which require large amounts of energy to overcome

Question 10

What are the three stages of free radical substitution?

Answer 10

Initiation
Propagation
Termination

Question 11

Why do Alkanes have a low reactivity?

Answer 11

Hydrocarbons are made from hydrogens and carbons only which have very close electronegativities meaning a very low polarity. They are usually symmetrical so the dipoles cancel out
Hydrocarbons have many C-C and C-H bonds which have high bond enthalpies so a lot of energy is needed to break them

Question 13

Explain how carbon monoxide can cause problems in terms of human health

Answer 13

Carbon monoxide is dangerous for humans to breathe in because it binds to the haemoglobin in the human blood meaning oxygen can’t be carried round the body to cells

Question 14

What is a property of a free radical?

Answer 14

Free radicals are very reactive

Question 15

What is homolytic fission?

Answer 15

Covalent bond is broken and each atom in the covalent bond takes one of the bonding electrons

Question 16

What is the role of UV radiation in the process of free radical substitution?

Answer 16

Provides energy needed for homolytic fission to occur (break covalent bond)

Question 17

What is the general formula of an Alkane?

Answer 17

CnH2n+2