hydrocarbons

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8 Terms

1
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what are the properties of alkanes?

  • saturated hydrocarbons

  • insoluble in water

  • generally unreactive

2
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why does the boiling point of alkanes increase as the length of the chain increases?

  • longer chain alkanes have more electrons than shorter chain alkanes which increases the strength of the london forces

  • longer chain alkanes have a greater surface area so there are more points along the chains where london forces can be formed

3
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why do branched alkanes have a lower boiling point than straight chain alkanes?

  • the branches prevent alkane molecules from getting closer together - and london forces are strongest over short distances

4
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what is the cracking of alkanes?

converts long chain hydrocarbons into short chain hydrocarbons and produces alkenes which are highly reactive material

5
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how is thermal cracking carried out?

  • requires a high temperature and high pressure

  • 450-900^celcius

  • 70 atm

  • makes short chain alkanes, alkenes and water

6
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what is a free radical?

a species with an unpaired pair of electrons

7
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how is thermal cracking carried out?

  • 450^celcius

  • 1-2 atm

  • aluminium oxide catalyst

  • products are often branched chain alkanes - useful for petrol as they combust efficiently

  • also produces cyclic alkanes and aromatic compounds

8
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describe the process of free radical substitution of alkanes

step 1: initiation

  • Cl2 (UV)→(heat) 2Cl*

step 2: propagation

  • Cl* + C2H6 → *C2H5 + HCl

  • C2H5 + Cl2 → C2H5Cl + Cl*

step 3: termination step

  • Cl* + Cl* → Cl2

  • C2H5 + Cl* → C2H5Cl

  • *C2H5 + *C2H5 → C4H10