alkenes

Question 1

what are alkenes?

Answer 1

alkenes are unsaturated organic compounds that contain double carbon-carbon bond(s)

Question 2

what is ethene’s
-full structure bond
-no. of carbon atoms
-molecular formula

Answer 2

2 carbon atoms
C2H4

Question 3

what is propene’s
-full structure bond
-no. of carbon atoms
-molecular formula

Answer 3

3 carbon atoms
C3H6

Question 4

what is butene’s
-full structure bond
-no. of carbon atoms
-molecular formula

Answer 4

4 carbon bonds
C4H8

Question 5

what are the chemical properties of alkenes?

Answer 5

combustion
alkenes can be used as fuel and can undergo incomplete or complete combustion
addition reaction
unsaturated alkenes can undergo addition reaction to form a single product. the double carbon-carbon bond will break to form two new single bonds (unsaturated to saturated)
bromination
it is to test for unsaturation and distinguish alkenes from alkanes
unsaturated=bromination occurs and reddish-brown solution decolourises
saturated=bromination does not occur and solution remains reddish-brown
hydrogenation
eg. margarine can be produced by adding excess hydrogen to unsaturated vegetable oil at 200 degrees celsius and in the presence of a nickel catalyst
addition polymerisation
at high temperature and pressure, and in the presence of a catalyst, unsaturated monomers join together to form a single large molecule(polymer)

Question 6

what is the state of saturated fats at room temperature?

Answer 6

they are usually solids at rtp

Question 7

what is the state of unsaturated fats at room temperature?

Answer 7

they are usually liquids at rtp

Question 8

what happens during addition polymerisation?

Answer 8

eg. formation of polyethene
one of the carbon-carbon double bonds in ethene monomer breaks and each monomer forms a single covalent bond with two other ethene monomers

Question 9

what can polyethene be used to make?

Answer 9

plastic bags and clingfilm

Question 10

why is plastic bad for the environment?

Answer 10

plastics are non-biodegradable and cannot be broken down by the bacteria in the soil
it can cause land and water pollution if not disposed properly
it causes air pollution when burnt (toxic gas is produced)

Question 11

what is cracking?

Answer 11

breaking down of long-chain hydrocarbons into smaller molecules

Question 12

what are necessary conditions for cracking?

Answer 12

high temp (600 degrees celsius) and an aluminum oxide (Al2O3) catalyst

Question 13

what is the importance of cracking?

Answer 13

produce short-chain alkenes
produce hydrogen gas
produce shorter chain alkanes such as petrol
however, not all cracking reactions will produce hydrogen gas as a product