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Module 4 - Core organic chemistry > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is an alkane?

A

A saturated hydrocarbon containing C and H bonds only

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2
Q

What is the general formula for an alkane?

A

CnH2n+2

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3
Q

Are alkanes bonds polar? Why?

A

They are non polar because hydrogen and carbon have similar electronegativities

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4
Q

What is the shape and angle of an alkane?

A

Tetrahedral 109.5 degrees

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5
Q

Describe the sigma bond in an alkane.

A

A covalent bond which has a direct overlap of the electron clouds of the bonding atoms

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6
Q

What type of intermolecular forces do alkanes have?

A

London forces because they are non polar

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7
Q

What happens to the boiling point as alkane chain length increases? Why?

A

The bp increases because there is more surface area and so more induced dipole-dipole interaction

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8
Q

Does a branched molecule have a lower or higher boiling point compared to equivalent straight chain? Why?

A

Lower bp because of the fewer surface area so less induced dipole-dipole interactions

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9
Q

Are alkanes soluble in water? Why?

A

Insoluble because hydrogen bonds in water are stronger than alkanes’ London forces

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10
Q

How reactive are alkanes?

A

Very unreactive

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11
Q

What reactions will alkanes undergo?

A

Combustion and reaction with halogens

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12
Q

What is complete combustion?

A

Combustion that occurs with plentiful of oxygen

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13
Q

What are the products of complete combustion?

A

CO2 and H2O

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14
Q

What is incomplete combsution?

A

Combustion in a limited supply of oxygen

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15
Q

What are the products formed in incomplete combustion?

A

H2O, CO2 and CO

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16
Q

What type of hydrocarbon are most likely to undergo incomplete combustion?

A

Longer chains

17
Q

How are halogenoalkanes formed from alkanes?

A

Radical substitution

18
Q

In the presence of what does alkanes react with halogens?

A

UV light

19
Q

What is homolytic fission?

A

Each of the bonded atoms takes one of the shared pair of electrons, each atom has a single unpaired electron (radical)

20
Q

What is heterolytic fission?

A

One of the bonded atoms takes both of the electrons from the bond

21
Q

What is an addition reaction?

A

A molecule is added to the unsaturated alkene

22
Q

What is a substitution reaction?

A

An atom or group of atoms is replaced by a different atom

23
Q

How would you calculate how much CO2 is produced during complete combustion of 1kg of C7H16?

A
  1. Calculate the amount of moles of C7H16 in 1kg of heptane (1kg=1000g)
  2. Write the balanced equation for the complete combustion of heptane and calculate the moles of CO2 produced
  3. Use the n=v/24 equation to find the volume of CO2 produced
24
Q

What are the steps for the bromination of methane?

A
  1. Initiation Br2 -> 2Br.
  2. Propagation CH4 + Br. -> CH3. +HBr
    CH3. + Br2 -> CH3Br + Br.
  3. Termination 2Br. -> Br2
25
Q

What are some limitations of radical substitution?

A
  1. Further substitution e.g another bromine radical can collide with bromomethane molecule substituting a further hydrogen atom
  2. Monosubstitution, if the carbon chain is longer we will get a mixture of monosubstituted isomers by substitution at different positions
26
Q

Name the process used to obtain kerosene from crude oil and explain why the process
works.

A
  • Fractional distillation
  • Fractions have different boiling points
27
Q

Explain why the straight chain isomer of C10H22 has a higher boiling point than any of its branched chain structural isomers

A
  • Branched chains have less surface contact
  • Branched chains have fewer van der Waals’ forces
28
Q

Explain why the straight chain isomer of C10H22 is converted by the petroleum industry into its branched chain isomers.

A

Branched chains have more efficient combustion

29
Q

Write an equation for the reaction between methane and bromine to make bromomethane and hydrogen bromide.

A

CH4+ Br2 → CH3Br + HBr

30
Q

Name one other bromine-containing organic product which is formed when methane reacts with bromine

A

Dibromomethane

31
Q

What is the name of the process used to convert long chain alkanes into more useful shorter chain alkenes?

A

Cracking

32
Q

What is the name of the process used to convert long chain alkanes into more useful shorter chain alkenes?

A

Cracking

33
Q

Why is ethane made in the radical substitution of methane and bromine?

A

Two CH3 radicals

Module 4 - Core organic chemistry (5 decks)

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