Chapter 13 - Alkenes

Question 1

What is the general formula for alkenes?

Answer 1

CnH2n

Question 2

How is a double bond formed?

Answer 2

Starts with 3 sigma bonds forming.
1 electron is left in the p-orbital.
Pi bond forms from the sideways overlap of 2 p-orbitals.

Question 3

What stops rotation in alkenes?

Answer 3

The pi bond locks the 2 carbons in position, so alkenes cannot be rotated.

Question 4

What is the shape around the carbons in the double bond and why?

Answer 4

Trigonal planar because theres 3 regions of electron density around each carbon, which repel each other, all in the same plane.

Question 5

What are uses of polypropene?

Answer 5

Children’s toys,
Packing crates
Guttering

Question 6

What are the uses of polyphenylethene aka polystyrene?

Answer 6

Packaging material
Food trays and cups
Because of its thermal insulating properties

Question 7

What is the downside of current disposal of waste polymers?

Answer 7

Very unreactive so are non-biodegradable, with negative environmental effects.

Question 8

What are the benefits of recycling polymers?

Answer 8

Reduces environmental impact by conserving fossil fuels and decreasing waste.

Question 9

What are the weaknesses of recycling polymers?

Answer 9

Polymers have to be sorted by type. They can’t be mixed because they would become unusable.

Question 10

What are the dangers of PVC (Polychloroethene) disposal?

Answer 10

High chlorine content and range of additives present make it hazardous.
When burnt it releases corrosive hydrogen chloride gas.

Question 11

How can polymers be used as fuel?

Answer 11

They can be burned to produce heat.

Question 12

What is feedstock recycling?

Answer 12

Chemical and thermal processes that can reclaim monomers and gases from waste polymers.

Question 13

What is a major advantage of feedstock recycling?

Answer 13

Able to handle unsorted and unwashed polymers.

Question 14

What are biodegradable polymers?

Answer 14

Polymers made from renewable sources and can be broken down by microbes.
Made from starch or cellulose.

Question 15

How is a sigma bond formed?

Answer 15

Head on overlap of orbitals of 2 bonding atoms,
With electron density centred around a line directly between the nuclei of bonding atoms.

Question 16

What is a pi bond?

Answer 16

A sideways overlap of 2 p-orbitals with electron density above and below the plane of bonding atoms.

Question 17

What is a reaction mechanism?

Answer 17

A series of steps that shows how a reaction takes place

Question 18

What is an electrophile?

Answer 18

An atom or group of atoms that is attracted to an electron-rich centre and accepts an electron pair.

Question 19

What atom or molecule is usually an electrophile?

Answer 19

Positive ions or molecules with an atom that has a δ+ charge

Question 20

How does a double bond attract electrophiles?

Answer 20

It represents a region of high electron density due to the presence of π electrons, which attracts electrophiles.

Question 21

Why are alkenes more reactive than alkanes?

Answer 21

Because the π bond electrons are more exposed than the σ bond electrons, so the π bond breaks more easily

Question 22

What is a monomer?

Answer 22

A small molecule that combines with many other monomers to form the polymer.

Question 23

What is a repeat unit?

Answer 23

The arrangement of atoms that occurs in the polymer structure over and over again.