AS Chemistry - Alkanes

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Define a hydrocarbon?
Compounds containing hydrogen and carbon only.
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Define saturated?
Containing single bonds only.
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Define molecular formula
The actual number of atoms of each element in a molecule.
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Define general formula
The simplest algebraic formula of any molecule of a homologous series.
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Define empirical formula
The simplest whole number ratio of atoms of each element in a compound.
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Define homologous series
A series of organic compounds having the same functional group but with each successive member differing by CH2.
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Define structural formula
Same molecular formula, different structural formula
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Define a radical
A species with an unpaired electron
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Define a substitution reaction
A reaction in which an atom or group of atoms is replaced with another atom or group of atoms
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Describe homolytic fission
The breaking of a covalent bond where the shared pair of electrons are split equally forming two radicals
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What is the general formula of an alkane?
CnH(2n+2)
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What is the general formula of a cycloalkane?
CnH2n
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Explain why alkanes are insoluble in water
Alkanes are non-polar molecules. Induced dipole-dipole interactions between alkane molecules and water molecules are weaker than the hydrogen bonds between water molecules
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Explain why alkanes have low boiling points
Alkanes are non-polar molecules. Very little heat energy is required to overcome the weak, induced dipole-dipole attractions, between alkane molecules.
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Describe and explain the trend in boiling points for alkanes with increasing chain length
As chain length increases boiling point increases because surface contact between molecules increases so more energy is required to break stronger induced dipole-dipole attractions between the molecules.
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Describe and explain the trend in boiling points for alkanes with increasing branching
As branching increases boiling point decreases because surface contact between molecules decreases so less energy required to break weaker induced dipole-dipole attractions between the molecules.
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Explain why alkanes are not very reactive
They are non-polar molecules.they contain only strong C-C and C-H single bonds which require a large amount of energy to break
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What are the products of complete combustion of an alkane?
CO2 and H20.
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What are the products of incomplete combustion of an alkane?
CO and H20
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Why is the combustion of alkanes an effective energy source?
Exothermic reaction (releases heat energy) and hydrocarbons have a high energy content (for a given mass of fuel)
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Describe the mechanism for the reaction of methane with bromine.
1. Initiation: uv light, Br2 = 2Br• homolytic fission 2. Propagation Br• + CH4 = HBr + •CH3, •CH3 + Br2 = CH3Br + Br• 3. Termination •CH3 + Br• = CH3Br, •CH3 + •CH3 = C2H6, Br• + Br• = Br2
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Explain why radical substitution is not a good method for the preparation of a single halogenoalkane?
Uncontrollable termination steps lead to a mixture of products. Further propagation steps on the mono-substituted product form poly-substituted halogenoalkanes.
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Other cards in this set

Card 2

Front

Define saturated?

Back

Containing single bonds only.

Card 3

Front

Define molecular formula

Back

Preview of the front of card 3

Card 4

Front

Define general formula

Back

Preview of the front of card 4

Card 5

Front

Define empirical formula

Back

Preview of the front of card 5
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