4.5.2 - alkanes Flashcards
what are alkanes
hydrocarbons that fit the general formula CnH2n+2
what are alkanes made of
simple molecules containing carbon and hydrogen atoms held together by covalent bonds
what does the start of the name of an alkane show
how many carbon atoms it has
what does the end of the name of an alkane show
ends in ‘—ane’ to show its an alkane
what is the formula of methane
CH4
what is the formula of ethane
C2H6
what is the formula of propane
C3H8
what is the formula of butane
C4H10
what is the formula of pentane
C5H12
what are the names of the first five alkanes
methane, ethane, propane, butane, pentane
what is the displayed formula
a diagram that shows the position of every atom and every bond
what is the structural formula
shows the structure of the molecule in one line
what is the molecular formula
only shows how many hydrogen and carbon atoms there are
what is the empirical formula
only shows the simplest whole number ratio of carbon to hydrogen
how are alkanes a homologous series
they all have:
- similar chemical reactions
- trends in physical properties (e.g. boiling points, viscosity or colour)
- the same general formula
what are isomers
molecules with the same molecular formula but a different structural formula
why are most alkanes used a fuel
they release a lot of energy when combusted
what two types of combustion can alkanes undergo
complete or incomplete
complete combustion:
occurs when there is excess oxygen
alkane + oxygen -> carbon dioxide + water
incomplete combustion:
occurs when there isn’t enough oxygen
produces carbon monoxide and soot
releases less energy so it makes the alkane less useful
the combustion of alkanes as fuels releases three significant pollutants into the atmosphere:
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
how do alkanes react with halogens
swapping one hydrogen atom for one halogen atom
what type of reaction is an alkane reaction with a halogen
a substitution reaction because they swap
what does the reaction between a halogen and alkane require
UV light because the alkane is pretty unreactive
