alkenes

Question 1

formula for alkenes

Answer 1

CnH2n

Question 2

are alkenes saturated or unsaturated

Answer 2

unsaturated

Question 3

what is a pi bond

Answer 3

indirect overlap of orbitals

Question 4

what is a sigma bond

Answer 4

simple covalent bond with direct overlap of orbitals

Question 5

why are alkenes more reactive than alkanes

Answer 5

-as it has a C=C
-double bonds have a high electron density where the electrons are localised between the C=C
-this makes them more reactive towards a strong electron acceptor

Question 6

what is an electrophile

Answer 6

something that likes negative charge

Question 7

what is hydragenation of alkenes

Answer 7

turns an alkene into an alkane

Question 8

what happens during hydragenation of alkenes

Answer 8

an addition reaction occurs when an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K

CH2=CH2 + H2 –> CH3CH3

Question 9

what is a halogenation

Answer 9

a rapid addition reaction will occur when an alkene reacts with a halogen
Alkene –> haloalkane
CH2=CH2 + Cl-Cl –>CH2ClCH2CL

Question 10

what is bromination

Answer 10

is used to show the presence of an alkene
-bromine turns from orange to colourless

Question 11

what happens during alkenes and hydrogen halides

Answer 11

-gas H halides and alkenes will react together at room temperature
-if alkene is a gas then the two gases mix together
-if the alkene is liquid, the hydrogen halide must be bubbled through
-alkenes can also react with concentration hydrobromic acid or hydrochloric acid

CH2=CHCH3 + HCl –> CH2ClCH2CH3

Question 12

what is hydration of alkenes

Answer 12

alkene reacted with steam in the presence of a phosphoric acid then an alcohol will form

CH2=CHCH3 + H2O –> CH2OHCH2CH3

Question 13

how does a molecule show isomerism

Answer 13

-if it has C=C
-if it has two different groups on each carbon

Question 14

what does a C=C bond do in isomerism

Answer 14

restricts rotation

Question 15

what is electrophillic addition

Answer 15

the addition of an electrophile to an alkene double bond, C=C

Question 16

what happens In electrophilic addition reactions with hydrogen halides

Answer 16

-H atom acts as an electrophile by accepting a pair of electrons from the C=C bond in the alkene
-The H-Br bond breaks heterolytically, forming a Br- ion
-This results in the formation of a highly reactive carbocation intermediate which reacts with the bromide ion, Br-