Chapter 12: Alkanes (12.1-12.2) Flashcards

1
Q

general formula of alkanes

A

CnH2n+2

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2
Q

alkanes are saturated hydrocarbons, what does this mean

A

alkanes have single covalent bonds and contain single carbon-hydrogen bonds only (sigma bonds)

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3
Q

properties of sigma bonds

A

formed from the overlap of orbitals directly between the bonding atoms
can rotate freely

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4
Q

shape and bond angle of alkane

A

tetrahedral

109.5

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5
Q

boiling point trends in straight-chain alkanes

A

as the carbon chain length increases, the boiling point increases
more electrons and more points of contact between molecules means strength of London forces between molecules increases. More energy is needed to break IMFs

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6
Q

boiling point trends in branched-chain alkanes

A

as branching in isomers increases, the boiling point decreases
fewer points of contact between molecules means strength of London forces decreases
less energy needed to break IMFs

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7
Q

solubility of alkanes

A

alkanes are non-polar molecules

not soluble in polar solvents (e.g. water). soluble in non-polar solvents (e.g. oil)

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8
Q

reactivity of alkanes

A

low reactivity
sigma bonds (C-C and C-H) are have high enthalpy (strong, hard to break)
C-C and H-H bonds are non-polar (making them less reactive)

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9
Q

what is a fuel

A

fuels are substances that can be burnt in oxygen to release heat energy

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10
Q

how does an alkane act as a fuel

A

although unreactive, many alkanes react exothermically with oxygen to make good fuels

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11
Q

alkane + oxygen –>

excess oxygen, complete combustion

A

CO2 (g) + H2O (l)

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12
Q

alkane + oxygen –>

excess alkane, incomplete combustion

A

CO (g) + H2O (l)

carbon only undergoes partial oxidation, unburnt carbon atoms can be released as carbon particles (soot)

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13
Q

dangers of carbon monoxide

A

toxic gas that binds with haemoglobin in red blood cells, preventing haemoglobin from carrying oxygen
difficult to detect: colourless and odourless

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14
Q

reactions of alkanes with halogens

A

alkane + halogen –> haloalkane + hydrogen-hailide

radical substitution, needs UV light to start

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15
Q

steps of radical substitution (alkane + halogen)

A

1) initiation. UV radiation provides energy for homolytic fission of halogen molecule to form 2 radicals
2) propagation. 2 reactions of radicals reacting with molecules to form a molecule and a new radical (radical will be on carbon a molecule or a lone halogen)
3) termination. 3 reactions of 2 radicals reacting to form a molecule

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16
Q

limitations of radical substitution for organic synthesis (production of organic molecules on an industrial level)

A

a large mixture of products can be formed:
Further substitution: the main product will still contain hydrogen atoms (easily replaced)
Structural isomers: for alkanes with a chain of 3 or more C atoms, substitution can take place at different points along the chain giving different structural isomers