Addition reactions of alkenes

Question 1

define the term addition reaction.

Answer 1

a reaction in which two molecules combine to form one molecule

Question 2

What happens when an alkene reacts with a halogen?

Answer 2

the alkene becomes saturated, with the pi bond breaking to form two new sigma bonds, one with each halogen molecule.

Question 3

explain why the pi bond breaks in addition reactions.

Answer 3

the pi bond contains a pair of shared electrons which are less under the control of the carbon atoms in the C=C bond than the tightly held electrons in the sigma bond. this does mean a double bond is stronger than a single bond, but not twice as strong. the pi bond is more easily broken to form two new single covalent bonds.

Question 4

what is the test for unsaturated hydrocarbons?

Answer 4

bromine water is added, and turns colourless from orange.

Question 5

what is a diol?

Answer 5

a compound containing two OH (alcohol) groups

Question 6

what is hydration?

Answer 6

involves the addition of water or steam, as an H and OH on the carbon atoms which previously had a double C=C bond

Question 7

what is halogenation?

Answer 7

involves the addition of a halogen

Question 8

what is hydrogenation?

Answer 8

involves the addition of hydrogen

Question 9

why can’t hydrogen halides be used as a test for double C=C bonds?

Answer 9

Because both reactants (hydrogen halide and alkene) and the products (halogenoalkane) and colourless