Chapter 12-Alkanes

Question 1

What type of bonding is present in alkanes?

Answer 1

Sigma bonds(single bonds)

Question 2

What is the shape and bond angle around alkanes?

Answer 2

Shape:Tetrahedral

Bond Angle:109.5°

Question 3

Describe fractional distillation

Answer 3

Mixture is heated up. Each substance has a different boiling point so rises to different points on the fractionating column. Separate substances cool through a condenser.

Question 4

What is the effect of chain length on boiling point and why?

Answer 4

As the chain length increases molecules have a larger surface area so more points of surface contact. This means London Forces are stronger so more energy is required to break them. This means the boiling point increases

Question 5

What is the effect of branching on boiling point of alkanes?

Answer 5

More branching decreases the surface area, meaning there are fewer surface points of contact. This means that London forces are weaker, and less energy is required to break them. The boiling point is therefore lower.

Question 6

Are alkanes reactive? Why?

Answer 6

Alkanes are unreactive. Their C-C bonds and C-H bonds are strong and non polar so they are difficult to break

Question 7

What is complete combustion?

Answer 7

Occurs in a plentiful supply of oxygen

Produces CO2 and H2O

Question 8

What is incomplete combustion?

Answer 8

Occurs in limited supply of oxygen
Always forms H2O
Could form CO or C(soot)

Question 9

Radical Substitution Reaction

Answer 9

A type of reaction used in halogenation of alkanes

Question 10

Initiation

Answer 10

Stage one of radical substitution reaction
Reaction started when bond in halogen molecule broken by homolytic fission.
Forms 2 halogen radicals

Question 11

Propagation

Answer 11

Stage 2 of radical substitution reaction
Step 1: Look at Notes
Step 2:Look at Notes

Question 12

What is the halogen radical in the propagation step?

Answer 12

Catalyst

Question 13

What is termination

Answer 13

Stage 3 of radical substitution reaction
2 radicals collide, forming a molecule with all electrons paired
For the combinations, look in the textbook

Question 14

Limitations of radical substitution (4 marks)

Answer 14

Further Substitution- Further substitution could continue until all the hydrogen atoms have been substituted. Results in a mixture of products. Not all of them useful
Substitution at different points in the carbon chain-the halogen could be in different points along longer chains, which we may not want