Alkenes Flashcards
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Where are Alkenes mainly obtained from?
cracking Alkanes
What is the general formula for Alkenes?
CnH2n
What does Unsaturated hydrocarbons mean?
Unsaturated: Carbon-Carbon double bonds (C=C)
Hyrdrocarbons: A compound contains only Hydrogen and carbon elements.
Why are Alkenes reactive?
- 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.
What are the prefixes used for Alkenes?
Eth,Prop,but
(Eat, Peanut, Butter)
What are the first few members of Alkenes?
Ethene, Propene, Butene
what is the chemical and structural forumal for Ethene?
Structural: C2H4
description: C=C covalently bonded to two hydrogen atoms respectively.
What is the chemical and structural formula for Propene?
Structure: C3H6
Structure: C=C-C and then Hydrogen atoms are bonded to the three carbons respectively.
What is the chemical and structural formula for Butene?
Chemical: C4H8
Structure: C=C-C-C and Hydrogen atoms resepctively added to each carbon atom
what are the reactions that Alkenes go through?
- Cracking
- Combustion
- Addition (Hydrogenation, Bromination, Polymerisation)
What is cracking?
Cracking is the process to break up large Alkanes into smaller useful molecules
Why is Cracking Important?
- 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.
What are the products from Cracking?
- Alkenes
- Hydrogen
- Small Alkene molecules
What conditions must be met in order for Cracking to take place?
- High Temperature (600 degrees)
- Solid Catalyst: Aluminium oxide or Silicon oxide or Porcelain chips.
What are the two possible pathways (equations) for Cracking?
- Large Alkane-> Smaller Alkane + Alkene
- C18H38-> C8H18 + C10H20
2. Large Alkane-> Alkene + Hydrogen - C18H38-> C18H36 + H2
What are the three addition reactions that Alkene go through?
- Hydrogenation
- Bromination
- Polymerisation
During a reaction, the Crabon-Carbon double bind will ipen wjich will allow yje addition if another molecule onto the Alkene.
What is hydrogeniation?
- Hydrogen is addded to Carbon-Carbon dluble bond at 200 degress with Nickle Catalyst
- Word equation: Alkene+ Hydrogen-> Alkane
- Example: Ethene + Hydrogen-> Ethane
What is Bromination?
- (aq) Bromine is added to carbon-carbon double bond
- Bromination is a test for unsaturation.
How to distinguish Alkanes (Saturated) and Alkenes (Unsaturated) from each other?
Alkenes are reactive hydrocarbons because they are unsaturated
- 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.
What is Addition Polymerisation?
- 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)
How to draw a polymer from a monomer?
- Redraw the monomer in the ‘H’ format
- Remove the C=C bonds and ass 2 more single bonds at the side/
- Example: propene-> Polypropene
What are the advantages of plastic?
- Light
- Corrosion resistant
- easil moulded into a varity of shapes
What is the disadvantages of plastics?
- 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.
