Alkenes

Question 1

Where are Alkenes mainly obtained from?

Answer 1

cracking Alkanes

Question 2

What is the general formula for Alkenes?

Answer 2

CnH2n

Question 3

What does Unsaturated hydrocarbons mean?

Answer 3

Unsaturated: Carbon-Carbon double bonds (C=C)
Hyrdrocarbons: A compound contains only Hydrogen and carbon elements.

Question 4

Why are Alkenes reactive?

Answer 4

• In Carbon-Carbon double bond
• Each Carnon atom in this type of bond is covalently bonded to three atoms only.
• Hence, a new atom can be added.

Question 5

What are the prefixes used for Alkenes?

Answer 5

Eth,Prop,but
(Eat, Peanut, Butter)

Question 6

What are the first few members of Alkenes?

Answer 6

Ethene, Propene, Butene

Question 7

what is the chemical and structural forumal for Ethene?

Answer 7

Structural: C2H4
description: C=C covalently bonded to two hydrogen atoms respectively.

Question 8

What is the chemical and structural formula for Propene?

Answer 8

Structure: C3H6
Structure: C=C-C and then Hydrogen atoms are bonded to the three carbons respectively.

Question 9

What is the chemical and structural formula for Butene?

Answer 9

Chemical: C4H8
Structure: C=C-C-C and Hydrogen atoms resepctively added to each carbon atom

Question 10

what are the reactions that Alkenes go through?

Answer 10

• Cracking
• Combustion
• Addition (Hydrogenation, Bromination, Polymerisation)

Question 11

What is cracking?

Answer 11

Cracking is the process to break up large Alkanes into smaller useful molecules

Question 12

Why is Cracking Important?

Answer 12

• Long chain hydrocarbons are broken down to increase the no. of short-chain hydrocarbons so as to meet the high demand for fuel and make more profit.

Question 13

What are the products from Cracking?

Answer 13

• Alkenes
• Hydrogen
• Small Alkene molecules

Question 14

What conditions must be met in order for Cracking to take place?

Answer 14

• High Temperature (600 degrees)
• Solid Catalyst: Aluminium oxide or Silicon oxide or Porcelain chips.

Question 15

What are the two possible pathways (equations) for Cracking?

Answer 15

1. Large Alkane-> Smaller Alkane + Alkene

• C18H38-> C8H18 + C10H20
  2. Large Alkane-> Alkene + Hydrogen
• C18H38-> C18H36 + H2

Question 16

What are the three addition reactions that Alkene go through?

Answer 16

• Hydrogenation
• Bromination
• Polymerisation

During a reaction, the Crabon-Carbon double bind will ipen wjich will allow yje addition if another molecule onto the Alkene.

Question 17

What is hydrogeniation?

Answer 17

• Hydrogen is addded to Carbon-Carbon dluble bond at 200 degress with Nickle Catalyst
• Word equation: Alkene+ Hydrogen-> Alkane
• Example: Ethene + Hydrogen-> Ethane

Question 18

What is Bromination?

Answer 18

• (aq) Bromine is added to carbon-carbon double bond
• Bromination is a test for unsaturation.

Question 19

How to distinguish Alkanes (Saturated) and Alkenes (Unsaturated) from each other?

Alkenes are reactive hydrocarbons because they are unsaturated

Answer 19

• When Reddish brown (aq) Bromine is added to unsaturated compound it will decolourise
• When reddish brown (aq) Bromine is added to staurated compound it will NOT decolourise.

Question 20

What is Addition Polymerisation?

Answer 20

• Akene molecules (Monomers) react with each other to form a kong molecule called a polymer.
• Conditions: High temp and pressure, catalyst
• Example: Ethene-> Poly(ethene)

Question 21

How to draw a polymer from a monomer?

Answer 21

• Redraw the monomer in the ‘H’ format
• Remove the C=C bonds and ass 2 more single bonds at the side/
• Example: propene-> Polypropene

Question 22

What are the advantages of plastic?

Answer 22

• Light
• Corrosion resistant
• easil moulded into a varity of shapes

Question 23

What is the disadvantages of plastics?

Answer 23

• Plastics produce a posinous gas such as carbon monoxide when they burn causing air pollution.
• Plastics are non-biodegradeable as bacteria do not break them down naturally. hence, more landfills need to be used to bury plastics which causes land pollution.