Reactions of alkenes

what are alkenes

unsaturated hydrocarbons of a homogolous series

what is the functional group for alkenes

C=C

what is the formula for alkenes

C_nH_2n

why can alkenes undergo addition reactions

because the carbon double bond can open up to allow the two carbon atoms to bond to atoms of another molecule

what happens when alkenes react with hydrogen(hydrogenation) and what are the conditions?

- an alkane is formed

- conditions : nickel catalyst and 150’C

what is hydrogenation used for

to manafacture margarine from vegetable oils

what happens when alkenes react with water vapour (hydration) and what are the conditions

- produces an alcohol

- conditions : phosphoric acid catalyst, high temps ( 330’C). pressure of 60-70 atmospheres

how do you separate the ethanol from the mixture of unreacted ethene and unreacted water after hydration

cool down the mixture and the ethene stays as a gas ( as it has a low bp) and the water and ethanol condense into liquid form

how do we separate the mixture of ethanol and water

use fractional distillation, ethanol will boil first as it has a slightly lower boiling point than water, then it evaporates and condenses and water remains in the flask

what happens when an alkene reacts with a halogen ( halogenation) and what are the conditions

- it will produce a halogenoalkane eg. C₂H₄ —→ C₂H₄Br₂

- conditions : room temp

what is the test we use to distinguish alkenes from alkanes

react an alkene with bromine water and shake it

the alkene will decoulourise the bromine water from orange, so the orange colour disappears

this happens as alkenes are more reactive than alkanes due to their C=C double bond