chapter 13 (alkenes)

Question 1

alkenes are unsaturated hydrocarbons, what does that mean

Answer 1

they have at least one C=C double bond

Question 2

the general formula of alkenes

Answer 2

CnH2n

Question 3

sigma bond

Answer 3

overlap of atomic orbitals directly between bonding atoms

Question 4

pie bond

Answer 4

sideways overlap of p orbitals above and below the C-C bond sigma bond

Question 5

how many bonds are used in the formation of sigma bonds

Answer 5

three

Question 6

how many pie and sigma bonds does a C=C double bond have

Answer 6

1 sigma and 1 pie

Question 7

does the pie bond permit rotation about the C=C double bond

Answer 7

no, it restricts it

Question 8

stereoisomers

Answer 8

they have the same structural formula AND molecular formula but different arrangements of atoms in 3D space

Question 9

name the two different forms of stereoisomerism

Answer 9

E/Z isomerism
optical isomerism

Question 10

requirements for E/Z isomerism to occur

Answer 10

the presence of a carbon to carbon double bond

two different groups should be attached to each of the carbons in the double bond

Question 11

in E/Z isomerism the atoms attached to the carbons of the double bond are given priority based on…

Answer 11

their atomic number

Question 12

z isomer

Answer 12

an isomer where the groups of higher priority are on the same side of the double bond

Question 12

z isomer

Answer 12

an isomer where the groups of higher priority are on the same side of the double bond

Question 13

e isomer

Answer 13

an isomer where the groups of higher priority are diagonally placed across the double bond

Question 14

requirements for a cis-trans isomerism to occur

Answer 14

there should be a C=C double bond

two different groups should be attached to each carbon of the double bond

one of the attached groups on each carbon must be the same

Question 15

cis isomer
trans isomer

Answer 15

for cis isomerism, identical groups are on the same side of the C=C double bond
in trans isomerism, identical groups are placed diagonally on the C=C double bond

Question 16

why are alkenes more reactive than alkanes

Answer 16

because the pie electrons of the double bond are more exposed than the sigma bonds as they are outside of the double bond.
so the pie bonds break readily and alkenes undergo reactions relatively easily

Question 17

addition reaction

Answer 17

when two reactants join together to form one product

Question 18

name four addition reactions that alkenes may undergo

Answer 18

halogenation reactions
hydrogenation reactions
reaction with hydrogen halides
hydration reactions

Question 19

what happens in hydrogenation reactions of alkenes
catalyst required for such reactions to take place

Answer 19

alkene reacts with hydrogen to form an alkane

a nickel catalyst

Question 20

what happens in halogenation reactions of alkenes

Answer 20

alkene reacts with a halogen to form a dihaloalkane

Question 21

test for the presence of a C=C double bond in an alkene

Answer 21

add bromine water dropwise
if a C=C bond is present, the bromine water decolorises from orange

Question 22

what happens in the reaction of alkenes with hydrogen halides

Answer 22

alkenes react with hydrogen halides to form a haloalkane

Question 23

if the alkene is unsymmetrical in it’s reaction with hydrogen halides, then how many possible products are formed

Answer 23

2

Question 24

what happens in the hydration reaction of alkenes
what catalyst is required in the reaction

Answer 24

alkenes react with steam to form alcohol

a phosphoric acid catalyst

Question 25

if the alkene is unsymmetrical in a hydration reaction, then how many possible products are formed

Answer 25

2

Question 26

which has a higher bond enthalpy between a sigma and a pie bond, and what does this indicate

Answer 26

a sigma bond has a higher bond enthalpy than a pie bond and this shows that a pie bond is weaker than a sigma bond. it breaks more readily

Question 27

electrophile

Answer 27

an electron acceptor

Question 28

in the electrophilic addition of alkenes to hydrogen halides, what causes the double bond in the alkene to break

Answer 28

the attraction between the partially positive hydrogen atom in the hydrogen halide and the electron pair in the pie bond

Question 29

in electrophilic addition of alkenes, the electrophile breaks by

Answer 29

heterolytic fission

Question 30

the major product is formed via the…………….

Answer 30

most stable carbocation intermediate

Question 31

the two ways that we determine the stability of a carbocation intermediate

Answer 31

the more alkyl groups attached to the carbocation intermediate, the more stable it is
or
the fewer hydrogen atoms attached to the carbocation intermediate, the more stable it is

Question 32

polymer

Answer 32

consists of many monomers joined together to make a long chain

Question 33

benefits for sustainability of processing waste polymers

Answer 33

waste polymers can be used as fuel by incinerating them to produce heat, which in turn generates heat to power turbines to produce electricity

feedstock recycling: reclaiming monomers from waste polymers which can be used as raw materials for the production of new polymers
recycling
PVC recycling

Question 34

environmental benefits of developing biodegradable and photodegradable polymers

Answer 34

bioplastics are made from plant-based materials, so they are renewable and sustainable

Question 35

biodegradable polymers

Answer 35

polymers that are broken down by bacteria into water, carbon dioxide and biological compounds

Question 36

photodegradable polymers

Answer 36

polymers that contain bonds which are weakened by absorbing light