Chapter 12 - Properties of Alkanes

Question 1

General Formula of Alkanes?

Answer 1

CnH2n+2

Question 2

What are sigma bonds?

Answer 2

Sigma bonds are formed from the overlap of orbitals directly between bonding atoms. Sigma bonds can freely rotate.

Question 3

Shape of Alkanes?

Answer 3

• Each carbon atom has four bonded pairs of electrons , repelling each other equally
• resulting in tetrahedral shape
• bond angle is 109.5degrees

Question 4

Properties of a straight chain that length increases?

Answer 4

Boiling points increases!

• more electrons and more points of contact
• strength of London forces increases
• more energy required to break the intermolecular forces

Question 5

Properties of a branched chain that length increases?

Answer 5

Boiling points decreases!

• fewer points of contact between molecules
• strength of London forces between the molecules decreases
• less energy required to break the intermolecular forces

Question 6

Are alkanes polar?

Answer 6

Alkanes are non polar molecules and will mix with non polar solvents. Non polar as there is little difference in electronegativity.

Question 7

What is produced in complete combustion?

Answer 7

carbon dioxide and water

Question 8

What is produced in incomplete combustion?

Answer 8

carbon monoxide, water, and soot

Question 9

Reaction of alkanes with halogens and the presence of UV radiation?

Answer 9

Radical substitution

Question 10

Radical substitution

Initiation Reaction -

Answer 10

Cl2 –> 2Cl. (Radicals)

Question 11

Radical substitution

Propagation reaction -

Answer 11

1. Cl. + CH4 –> HCl + .CH3

2. .CH3 + Cl2 –> CH3CL + Cl.

Question 12

Radical substitution

Termination reaction -

Answer 12

1. Cl. + Cl. –> Cl2
2. .CH3 + Cl. –> CH3CL
3. .CH3 + .CH3 –> C2H6

Question 13

Why in radical substitution can different structural isomers form?

Answer 13

Substitution can take place at different positions along the carbon chain