Alkanes Flashcards
general formula for alkanes?
Cn H2n+2
what type of molecule are all alkanes
simple molecular
describe + explain trend in alkane boiling point
as the straight chain gets longer, the boiling point increases
- longer chain = larger surface area contact
- large SA contact = stronger VdW forces = high boiling point
what is crude oil
a mixture of different length hydrocarbons
what method is used to separate different alkanes in crude oil
fractional distillation
- crude oil is vaporised and put into a tower which is hotter a the bottom and colder at the top
- as vapour rises it cools and will condense at different heights as they have different boiling points
- larger molecule = lower down the column it condenses
what happens to the hydrocarbons as the carbon chain gets longer
- become more viscous (thick)
- harder to ignite
- less volatile
- have higher boiling points
- have stronger VdW forces between molecules
what method do you use to split longer hydrocarbons into shorter ones
thermal cracking and catalytic cracking
what are the conditions of thermal cracking
- high temperature
- high pressure
what does thermal cracking produce
- produces a high percentage of alkenes and straight-chain alkanes
what are the conditions of catalytic cracking
- high temperature
- slight/moderate pressure
- zeolite catalyst
what does catalytic cracking produce
- produces motor fuels ( short chain alkanes), aromatic hydrocarbons and cycloalkanes
what products form from the complete combustion of alkanes?
carbon dioxide and water
what products form from the incomplete combustion of alkanes?
carbon and/or carbon dioxide
why is complete combustion more cost-effective than incomplete combustion
- complete combustion is more exothermic
name 5 pollutants from incomplete combustion?
- carbon monoxide
- carbon particulates
- unburnt hydrocarbons
- nitrogen di/oxide(s)
- sulfur dioxide
how is carbon monoxide made , what problems does it cause and how is the problem solved
- formed by incomplete combustion of carbon containing fuels
- toxic gas
- solved by catalytic converters (in cars)
how are carbon particulates made , what problems do they cause and how is the problem solved
- formed by incomplete combustion of carbon containing fuels
- can cause respiratory problems
- solved by ensuring there’s a good supply of oxygen when burning fuels
how are unburnt hydrocarbons made , what problems do they cause and how is the problem solved
- formed by hydrocarbons not burning
- causes photochemical smug
- solved by catalytic converters (in cars)
how is nitrogen di/oxide(s) made , what problems does it cause and how is the problem solved
- combustion of nitrogen and oxygen in the air at high temperatures
- causes acid rain (when reacted with water)
- solved by catalytic converters (in cars)
how is sulfur dioxide made , what problems does it cause and how is the problem solved
- formed by combustion of sulfur containing compounds in fuels
- causes acid rain (when reacted with water)
- solved by flue gas desulfurization
how does flue gas desulfurization work
Removing sulfur compounds by reacting them with limestone (CaCO3) or lime (CaO)
what are the equations for flue gas desulfurization
CaCO 3(s) + SO 2(g) → CaSO 3(s) + CO
CaO + SO2→ CaSO3
what is a catalytic converter
a catalytic converter changes harmful compounds from an engine’s emissions into safe gases, like steam.
features of a catalytic converter + link to function
- honey comb structure = increases the surface area
- made of a ceramic material = withstands high temperatures inside the combustion engine
- honeycomb has thin coat of platinum, palladium, rhodium = reduces cost (thin)
nitrogen combustion equation
N₂ + O₂ → NO/NO₂/NO₃/2NO
