S3 Chemistry > Alkanes > Flashcards

Alkanes Flashcards

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1
Q

What is a homologous series?

A

Family of compounds which have same general formula, similar chemical properties, show gradation in physical properties and successive members differ by CH2 unit.

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2
Q

What are some examples of a homologous series?

A

Alkanes
Alkenes
Alcohols
Carboxylic acids

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3
Q

What are functional groups?

A

Reactive group within a compound.

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4
Q

What are hydrocarbons?

A

Compounds that contain only carbon and hydrogen.

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5
Q

What is the agreed international language of chemistry for naming organic compounds?

A

IUPAC system

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6
Q

What is general formula?

A

Algebraic formula that describes any member of homologous series.
E.g. butane = CnH2n+2

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7
Q

What is empirical formula?

A

Simplest ratio of atoms of each element in compound.
E.g. butane = C2H5

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8
Q

What is molecular formula?

A

Actual number of atoms of each element in molecule, with any functional group indicated.
E.g. butane = C4H10

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9
Q

What is condensed structural formula?

A

Shows atoms carbon by carbon, with attached hydrogens and functional groups.
E.g. butane = CH3CH2CH2CH3

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10
Q

What is structural formula (displayed formula)?

A

Shows how all atoms are arranged and all bonds between them.
E.g. butane =
H H H H
/ / / /
H - C - C - C - C - H
/ / / /
H H H H

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11
Q

What is skeletal structure?

A

Shows skeletal structure of carbon.
E.g. butane = . _ . _ . _ .

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12
Q

What is the general formula for the alkanes?

A

CnH2n+2

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13
Q

What is a saturated hydrocarbon?

A

Contains no C = C or C triple bonds.

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14
Q

What are all the alkanes?

A

Methane
Ethane
Propane
Butane
Pentane
Hexane

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15
Q

How many carbons does methane have?

A

1

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16
Q

How many carbons does ethane have?

A

2

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17
Q

How many carbons does propane have?

A

3

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18
Q

How many carbons does butane have?

A

4

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19
Q

How many carbons does pentane have?

A

5

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20
Q

How many carbons does hexane have?

A

6

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21
Q

What are the steps to naming branched molecules?

A
  1. Count carbon atoms in longest continuous chain.
  2. Decide type of molecule.
  3. Number carbons in longest carbon chain, if more than 1 longest chain pick one with most side-chains.
  4. Side-chains added as prefixes at start of name, put in alphabetical order, with number of carbon each attached to.
  5. If more than 1 identical side-chain or functional group, use di-, tri-, or tetra- before part of name, ignore when working out alphabetical order.
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22
Q

What are structural isomers?

A

Molecules which have same molecular formula but different structural formula.

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23
Q

What are geometric isomers?

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A

Molecules with same structural formula but different arrangement of atom due to presence of one or more C=C bond.

24
Q

What are the three types of structural isomers?

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A

Chain isomers
Position isomers
Functional group isomers

25
What are chain isomers?
Have different arrangement of carbon skeleton, some straight chains and others branched chains.
26
What is an example of a chain isomer?
Butane and methylpropane.
27
What are position isomers?
Have same skeleton and same atoms or groups of atoms attached. Difference is atom or groups of atoms attached to different carbon atom.
28
What is an example of a positional isomer?
1-chlorobutane and 2-chlorobutane.
29
What are functional group isomers?
Have atoms arranged into different functional groups.
30
What is an example of a functional group isomer?
Propanol and propanone (acetone).
31
Why does the physical state of alkanes change?
Not much different in electronegativity between C and H, so hardly any bond polarity. Only attraction between one molecule and neighbour will be van der Waal’s forces. Force will increase as molecule gets bigger, therefore boiling point increases. Longer the alkane chain, large the Mr, more electrons, stronger van der Waal’s forces.
32
Why does the physical state of alkanes change with branched chains?
More branched chain is, lower boiling point. Branched chains cannot lie close together like straight chained molecules. Weaker van der Waal’s forces results in lower boiling point.
33
Why will the only EMF’s in alkanes be van der Waal’s forces?
Alkanes are non-polar.
34
What does alphatic mean?
Straight chains.
35
What is complete combustion?
When fuel burnt in plentiful supply of oxygen.
36
What is incomplete combustion?
When fuel burnt in limited supply of oxygen.
37
What harmful products are produced from the combustion of alkane fuels?
Carbon monoxide Carbon (soot) Unburned hydrocarbons Oxides of nitrogen Oxides of sulfur
38
What is the percentage increase of CO2 in our atmosphere due to the combustion of organic compounds?
0.03% - 0.04%
39
What is the role of a catalytic convertor in a motor vehicle?
Remove pollutants by getting them to react with one another to form harmless products.
40
What does a catalytic convertor contain?
Platinum or rhodium alloy catalyst.
41
What colour flame is produced during complete combustion?
Orange flame.
42
What colour flame is produced during incomplete combustion?
Sooty, orange flame.
43
When does the substitution reactions of alkanes with halogens occur?
In presence of UV light.
44
What is the general equation for the substitution reactions of alkanes with the halogens?
Alkane + Halogen > Halogenalkanes + Hydrogen halide
45
What can be said about the hydrogen atom which is replaced in a substitution reaction of an alkane with a halogen?
No way of determining which hydrogen atom is replaced.
46
What is a substitution reaction?
Replacing one atom or group of atoms with a different atom or group.
47
What is a free radical?
Species which has single unpaired electron.
48
What is photochemical reaction?
Reaction occurring in presence of UV light.
49
What is homolytic fission?
When bond breaks with one electron going to each atom (forms radicals).
50
What is heterolytic fission?
When bond breaks it’s the two electrons going to one atom in bond.
51
What are the 3 stages of substitution reactions between alkanes and halogens?
Initiation Propagation Termination
52
What happens in the initiation stage of the substitution reactions between alkanes and halogens?
UV light breaks halogen molecules into free radicals. Provides energy to break bond.
53
What is an example of an equation for the initiation stage of the substitution reactions between alkanes and halogens?
Cl2 > 2Cl .
54
What happens in the propagation stage of the substitution reactions between alkanes and halogens?
Halogen radicals react with alkanes in chain reaction where halogen radicals acts as catalyst.
55
What is an example of the equations for the propagation stage of the substitution reactions between alkanes and halogens?
Step 1 - CH4 + Cl . > . CH3 + HCl Step 2 - . CH3 + Cl2 > CH3Cl + Cl .
56
What happens in the termination stage of the substitution reactions between alkanes and halogens?
When any two free radicals meet, must react to form molecule. Removes free radicals and stops chain reaction.
57
What is an example of the equations for the termination stage of the substitution reactions between alkanes and halogens?
2 . CH3 > CH3-CH3 . CH3 + Cl . > CH3Cl
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