Module 4 - Alkenes

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons that contain
at least one C=C bond made up of a 𝜋
bond and a 𝜎 bond

Question 2

What is the general formula of
alkenes?

Answer 2

CnH2n

Question 3

How is a 𝜋 bond formed?

Answer 3

Electrons in the adjacent p orbitals
overlap above and below the carbon
atoms. They can only be made after a 𝜎
bond is formed

Question 4

What bond restricts the
rotation of carbon atoms?

Answer 4

𝜋 bond

Question 5

What is the angle and shape
of a double bond?

Answer 5

Trigonal planar
120°

Question 6

Are they more or less reactive
than alkanes? Why?

Answer 6

More reactive due to high electron
density of double bond and the fact the
pi-bond is slightly easier to break

Question 7

What intermolecular forces of
attraction do they have?

Answer 7

Only London forces due to non-polar
bonds

Question 8

Are they soluble in water?
Why?

Answer 8

No, non-polar bonds

Question 9

Write an equation for the
complete combustion of
pent-2-ene

Answer 9

CH3CH=CHCH2CH3 + 7½O2→ 5CO2+ 5H2O

Question 10

What are the types of isomers
that can be formed using
alkenes?

Answer 10

E/Z isomers - due to the restricted
rotation
Cis-trans isomers - if two of the same
substituents are attached to each carbon

Question 11

What is an electrophile?

Answer 11

Species that are electron pair acceptors

Question 12

What is the most stable type of
carbocation intermediate?
Why?

Answer 12

Alkyl groups have a positive inductive
effect, so the most stable carbocation is
the one bonded to the most other carbon
atoms i.e. A tertiary carbocation

Question 13

Major products will be formed
from which kinds of
carbocations?

Answer 13

Tertiary (or the most stable available)

Question 14

What conditions are needed
for the electrophilic addition of
H2O to an alkene? What is this
type of reaction called?

Answer 14

Steam in the presence of an acid catalyst,
usually phosphoric acid
Reaction is called hydration

Question 15

What are the product(s) of the
hydration reaction?

Answer 15

An alcohol

Question 16

What conditions are needed
for the electrophilic addition of
a hydrogen halide to an
alkene?

Answer 16

Hydrogen halide gases must be at room
temperature

Question 17

What is the reaction called
when a halogen is added to
alkene?

Answer 17

Halogenation

Question 18

How does a molecule with a non-polar bond react as if it is an
electrophile?

Answer 18

C=C double bond with a high electron
density induces a temporary dipole in the
halogen molecule → δ+ atom attracted
to double bond

Question 19

How can an alkene be
converted into alkane? What is
the reaction called and what
are the required conditions?

Answer 19

Alkene + hydrogen = Alkane
Hydrogenation
Conditions → 150°C, nickel catalyst

Question 20

What is an addition polymer?

Answer 20

Many monomers bonded together via
rearrangement of bonds without the loss
of any atom or molecule

Question 21

What are monomers? What
form do they usually take?

Answer 21

Molecules which combine to form a
polymer
Usually have a C=C bond which breaks
to leave a repeating pattern

Question 22

What are the ways in which
plastics can be disposed?

6 points

Answer 22

● Landfill
● Combustion
● Electricity generation
● Reuse
● Recycle
● Organic feedstock

Question 23

What are the disadvantages of
recycling?

Answer 23

● Plastics must be sorted into different types
● Expensive
● Labour intensive
● Requires high technology

Question 24

How does photodegradable
polymers break down?

Answer 24

They are broken down chemically using
energy with wavelengths similar to light.
Once the break down begins it is not
possible to stop the process

Question 25

Explain what happens in
organic feedstock

Answer 25

Plastics are separated and broken down into
small organic molecules through a series of
reaction. The molecules can then be used
produce plastics and in other industries