12 alkanes Flashcards
define hydrocarbon
compounds containing carbon and hydrogen only
define saturated compounds
compounds containing single bonds only
define alkane
saturated hydrocarbons that contain only C-C and C-H single bonds
what is the general formula of an alkane?
C n H 2n+2
describe boiling points in alkanes
boiling points increase as carbon chain length increases
boiling points decrease when only branching increases
both affect induced dipole dipole forces
name a process for separating an alkane from a mixture of compounds
fractional distillation
outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions
- fractions have different boiling points
- depending on carbon chain length
- very hot at bottom of column and cooler at top
- longer molecules with higher bp condense at the bottom and smaller molecules with lower bp condense at the top
define fractions
mixtures of hydrocarbons with the same boiling point
what does cracking do?
converts long chain molecules into shorter chain molecules
why do oil companies need to crack heavy fractions?
smaller chain molecules are in higher demand
what are the two types of cracking?
thermal
catalytic
how does cracking convert long chain molecules into shorter chain molecules?
by breaking the C-C bonds
what do thermal and catalytic cracking produce high % of?
thermal: alkenes
catalytic: cycloalkanes and branched alkanes
give the conditions for thermal cracking
700-1200K
7000kPa
give the conditions for catalytic cracking
720K
100kPa
zeolite catayst
what is combustion in alkanes?
reaction with oxygen that releases energy
what are the two types of combustion?
incomplete
complete
give the conditions for both complete and incomplete combustion
complete: plentiful supply of oxygen
incomplete: limited supply of oxygen
what does complete combustion form?
CO2 and H2O
what does incomplete combustion form?
C or CO2 and H2O
all hydrocarbon based fuels deriving from crude oil may produce pollutants when combusted. name the pollutants
CO2 (g)
H2O (l)
CO (g)
C (s)
SO2 (g)
oxides of nitrogen
unburnt hydrocarbons
why is CO2 a pollutant?
causes global warming
why is H2O (l) a pollutant?
is a greenhouse gas
why is CO (g) a pollutant?
is toxic
why is C (s) a pollutant?
can damage the lungs
why is SO2 (g) a pollutant?
can form acid rain
why are oxides of nitrogen pollutants?
can form acid rain
why are unburnt hydrocarbons pollutants?
toxic and can cause cancer if inhaled
what are two methods of reducing pollution?
flue gas desulfurisation
catalytic converters
explain the two methods of desulfurisation
- CaO (s) + 2H2O (l) + SO2 (g) -> 0.5O2 -> CaSO4.2H2O (s)
- CaCO3 (s) + 0.5O2 (s) + SO2 (g) -> CaSO4 (s) + CO2 (g)
what can calcium sulphate be used to make?
plaster for building
what are catalytic coverters?
parts of modern car exhausts that convert harmful gases into less harmful ones
what do catalytic converters look like?
honeycomb structure
made of platinum and rhodium metals
why do catalytic converters have a honeycomb struture?
to increase surface area and rate of reaction
what three harmful compounds do catalytic converters convert into less harmful compounds?
No
CO
unburnt hydrocarbons
what is the equation for how catalytic converters convert NO and CO into less harmful gases?
2NO + 2CO -> 2CO2 + N2
what are the products when catalytic converters convert NO and unburnt hydrocarbons into less harmful gases?
N2 CO2 and H2O
