4.5.2 - alkanes

Question 1

what are alkanes

Answer 1

hydrocarbons that fit the general formula CnH2n+2

Question 2

what are alkanes made of

Answer 2

simple molecules containing carbon and hydrogen atoms held together by covalent bonds

Question 3

what does the start of the name of an alkane show

Answer 3

how many carbon atoms it has

Question 4

what does the end of the name of an alkane show

Answer 4

ends in ‘—ane’ to show its an alkane

Question 5

what is the formula of methane

Answer 5

CH4

Question 6

what is the formula of ethane

Answer 6

C2H6

Question 7

what is the formula of propane

Answer 7

C3H8

Question 8

what is the formula of butane

Answer 8

C4H10

Question 9

what is the formula of pentane

Answer 9

C5H12

Question 10

what are the names of the first five alkanes

Answer 10

methane, ethane, propane, butane, pentane

Question 11

what is the displayed formula

Answer 11

a diagram that shows the position of every atom and every bond

Question 12

what is the structural formula

Answer 12

shows the structure of the molecule in one line

Question 13

what is the molecular formula

Answer 13

only shows how many hydrogen and carbon atoms there are

Question 14

what is the empirical formula

Answer 14

only shows the simplest whole number ratio of carbon to hydrogen

Question 15

how are alkanes a homologous series

Answer 15

they all have:
- similar chemical reactions
- trends in physical properties (e.g. boiling points, viscosity or colour)
- the same general formula

Question 16

what are isomers

Answer 16

molecules with the same molecular formula but a different structural formula

Question 17

why are most alkanes used a fuel

Answer 17

they release a lot of energy when combusted

Question 18

what two types of combustion can alkanes undergo

Answer 18

complete or incomplete

Question 19

complete combustion:

Answer 19

occurs when there is excess oxygen
alkane + oxygen -> carbon dioxide + water

Question 20

incomplete combustion:

Answer 20

occurs when there isn’t enough oxygen
produces carbon monoxide and soot
releases less energy so it makes the alkane less useful

Question 21

the combustion of alkanes as fuels releases three significant pollutants into the atmosphere:

Answer 21

CARBON DIOXIDE
- forms directly from the combustion of the alkanes fuel
- a greenhouse gas that traps heat in the atmosphere and causes climate change

NITROGEN OXIDES
- this family of compounds form when nitrogen from the air combusts
- usually nitrogen doesn’t combust but car engines are really hot
- they dissolve in rainwater to form acid rain, which corrodes structures and it harmful to plant and aquatic life

SULPHUR DIOXIDE
- forms when sulphur impurities in the fuel combust
- like nitrogen oxides, it also dissolves in rainwater to form acid rain

Question 22

how do alkanes react with halogens

Answer 22

swapping one hydrogen atom for one halogen atom

Question 23

what type of reaction is an alkane reaction with a halogen

Answer 23

a substitution reaction because they swap

Question 24

what does the reaction between a halogen and alkane require

Answer 24

UV light because the alkane is pretty unreactive