Alkanes Flashcards

1
Q

Give the definition of a functional group

A

Part of a compound responsible for the chemical reactions

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2
Q

What is the definition for alkanes?

A

Naturally occurring hydrocarbons formed from crude oil

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3
Q

What reaction is most common for alkanes due to their unreactivity?

A

Combustion reactions

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4
Q

Give the definition of a sigma bond

A

A bond formed by the lengthways overlap of orbitals directly between two bonding atoms

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5
Q

Is a sigma bond covalent?

A

Yes

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6
Q

What are the strongest type of covalent bond?

A

C-C and C-H bonds, have a high bond enthalphy, are sigma bonds

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7
Q

What is the equation for complete combustion of alkanes?

A

Alkane + Oxygen —> Carbon Dioxide + Water
When there is an excess supply of oxygen

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8
Q

What is the equation for incomplete combustion of alkanes?

A

Alkane + Oxygen —> Carbon Monoxide + Water
OR
Alkane + Oxygen —> Carbon + Hydrogen
Both when there is a limited supply of oxygen

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9
Q

Is it possible to see CO2 and C or CO in an incomplete combustion equation?

A

Yes - mostly seen in MCQs

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10
Q

Why is CO a toxic gas?

A

CO bonds to haemoglobin which reduces blood oxygen concentration

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11
Q

What can covalent bonds be broken by?

A

Homolytic fission or heterolytic fission

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12
Q

What is the definition of homolytic fission?

A

Each bonding atom receives one electron from the covalent bond, forming two radicals

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13
Q

What is a radical?

A

A species with an unpaired electron

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14
Q

What is the overall general equation for free radical substitution?

A

Halogen + alkane —> Haloalkane + hydrogen halide

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15
Q

What type of reaction is a free radical substitution reaction?

A

A substitution reaction

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16
Q

Is it possible for free radical substitution reactions to continue until all hydrogen atoms are replaced by halogens?

17
Q

What condition will there need to be for free radical substitution?

18
Q

What is the reagent for a free radical substitution reaction?

A

Halogen molecule

19
Q

What is the initiation step of free radical substitution?

A

Stage 1 - Halogen molecule broken into two free radicals

20
Q

What is the propagation step for free radical substitution?

A

Stage 2 - 1st propagation - Alkane + Halogen radical —> alkyl radical + hydrogen halide

2nd propagation - alkyl radical + halogen molecule —> Haloalkane + halogen radical

21
Q

What is the termination step for free radical substitution?

A

Stage 3 - Two radicals collide to form a neutral molecule; two halogen radicals, a halogen radical and an alkyl radical, or two alkyl radicals

22
Q

What are the issues with free radical substitution?

A

Yield is low because; further substitution causes a mixture of products/ different termination steps form a mixture of products and substitution can occur in different positions meaning position isomers are formed

23
Q

Why would further substitution occur in a free radical substitution reaction and how could we reduce it?

A
  • Excess of halogen - chance of further substitution reduced by an excess of alkanes
24
Q

What type of reaction is the initiation step?

A

Photochemical - absorbs UV light to break covalent bonds

25
Q

Is any more energy needed for further reactions after the initiation step?