alkanes Flashcards
what is the trend in boiling points for straight chain alkanes
as the chain length increases, the surface area contact increases
stronger Van Der Waals forces between the molecules
boiling point increases
trend in boiling points for isomers
boiling point decreases
branched chain isomers have less surface area contact between the molecules
therefore fewer Van Der Waals forces between the molecules
what is crude oil
a complex mixture consisting mainly of alkanes, cycloalkanes and aromatics
what is distillation
separates mixtures of miscible liquids via a difference in boiling points
how does fractional distillation work
crude oil is vaporised
the vapour is passed into a tower with a negative temperature gradient
the vapour rises as it cools
molecules will condense at different heights as they have different boiling points
larger molecules condense lower down the column
this produces fractions
what is a fraction
mixtures of hydrocarbons with similar boiling points
why does a boiling point increase
an increase in Mr
increased surface area contact
longer carbon chain properties:
more viscous
higher boiling point
less volatile
stronger Van Der Waals forces between molecules
why are larger hydrocarbons cracked
as they are in excess, and to supply the demand for shorter hydrocarbons
what is cracking
breaking strong c-c covalent bonds
thermal cracking properties
high temperatures (1000 K)
high pressure (7000 kPa)
forms a high percentage of alkenes and straight chain alkanes
catalytic cracking properties:
high temperature (720 K)
moderate pressure (100-500 kPa)
high percentage motor fuels (branched alkanes), aromatic hydrocarbons, cycloalkanes
what are the 5 types of pollutants
carbon monoxide, carbon, unburnt hydrocarbons, NO/ NO2, sulfur dioxide
what is the cause, problem and solution for carbon monoxide
c- incomplete combustion
p- toxic
s- catalytic converter
what is the cause, problem and solution for carbon
c- incomplete combustion
p- respiratory problems
s- good supply of oxygen
what is the cause, problem.and solution for unburnt hydrocarbons
c- not burnt at all
p- photochemical smog
s- catalytic converter
what is the cause, problem and solution to NO/NO2
c- combustion of N2 in the air with O2
p- reacts with water in the air to form acid rain
s- catalytic converter
what is the cause, problem and solution of sulfur dioxide
c- combustion of sulfur containing compounds
p- forms acid rain
s- flue gas desulfurisation
what is flue gas desulfurisation
removes SO2 from gases emitted by fossil fuel power plants
CaO(s) +SO 2(g) → CaSO 3(s)
how does a catalytic converter work
dangerous polluting gases react to produce less harmful gases
N2(g) + O2(g) →2NO(g)
honeycomb structure
ceramic materials
coated in a metal catalyst such as palladium, platinum, rhodium
