Organic Chemistry: Alkanes Flashcards
What is a hydrocarbon?
A molecule made up of carbon and hydrogen only.
What is a functional group?
A group of atoms responsible for the characteristic reactions.
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound.
Define homologous series.
A family of compounds that have the same functional group and general formula
But a different C chain length
Define structural formula
The arrangement of the atoms.
Define molecular formula
The actual number of atoms present in each element in a compound
What are saturated hydrocarbons?
Hydrocarbons with single carbon-carbon bonds only.
What are unsaturated hydrocarbons?
Unsaturated hydrocarbons contain one or more double carbon-carbon bonds only.
Define structural isomers
Compounds with the same molecular formula but a different structural formula.
Define stereoisomers
Compounds with the same structural formula but a different arrangement of atoms in space
Shape of alkane
Bond angle of alkane
Tetrahedral
109.5
Polarity of alkanes
C and H have similar electronegativities = non-polar
Structure and bonding of alkanes
Simple molecular
Weak intermolecular van Der Waals forces
Solubility of alkanes
Not soluble
H bonds in water are stronger than VDWs
What are chain isomers?
Same functional group
Same molecular formula
Varying chain of carbon atoms
What are position isomers?
Same molecular formula
Same functional group
Functional group is attached at a different position
What are functional group isomers?
Same molecular group
Different functional group
What is the trend in the boiling point of alkanes?
As length of carbon chain increases, the boiling point of the alkane increases
More electrons = stronger VDWs forces = more energy required to overcome
What is the trend in boiling point in branched alkanes?
As the number of branches increases, the boiling point decreases
There are fewer points of contact between the molecules = VDWs forces become weaker = require less energy to overcome
Explain the fractional distillation of crude oil
Crude oil is vapourised and is introduced at the bottom of the fractionating column
Vapours rise causing a temperature gradient (hottest at bottom + coolest at top)
Different alkanes = different boiling points = different fractions at which they condense at
Hydrocarbons with the lowest boiling points don’t condense and are drawn off as gases at the top
Hydrocarbons with the highest boiling points don’t vaporise at all and are collected at the base as thick residue
What are the two types of cracking?
Catalytic Cracking
Thermal Cracking
Describe thermal cracking.
Very high temperature
Very high pressure
Produces alkanes and mainly alkenes (used to make polymers)
Describe catalytic cracking
High temperature
A slight pressure
In the presence of zeolite
Produces cyclic alkanes, branched alkanes and aromatic hydrocarbons
What are the products of complete combustion?
Carbon dioxide and water
What are the products of incomplete combustion?
Carbon monoxide and water
What are the solid products of incomplete combustion?
Carbon and water
Why does incomplete combustion occur?
Due to a limited supply of oxygen
Unburned hydrocarbons
Effect of pollutant
Production
Effect of pollutant: Low-level ozone (respiratory problems)
Production: Reacts with NOx to form low level ozone
Carbon Dioxide
Effect of pollutant
Production
Effect of pollutant: Global warming
Production: Combustion of fuels
Carbon Monoxide
Effect of pollutant
Production
Effect of pollutant: Toxic gas
Production: Incomplete combustion of fuels in limited O supply
Carbon
Effect of pollutant
Production
Effect of pollutant: Respiratory problems
Production: Incomplete combustion of fuels in very limited O supply
NOx
Effect of pollutant
Production
Effect of pollutant: Acid rain + photochemical smog
Production: O2 and N2 react at high temp in the engine
SO2
Effect of pollutant
Production
Effect of pollutant: Acid rain
Production: S from fuel impurities react with O2 from air
What is the mechanism called of turning an alkane into an halogenoalkane?
Free radical substitution
Reagant and conditions of free radical substitution
Halogen
UV light
What are the three steps of free radical substitution?
Initiation
Propagation
Termination
What are catalytic converters?
Remove CO and NOx in cars
Contain honeycomb structure (large surface area) coated with a thin layer of Pd/Pt/Rh metal
Why is a thin layer of Pd/Pt/Rh metal used?
Reduce cost
Removal of NO and CO
2NO + 2CO -> 2CO2 + N2
Removal of unburnt hydrocarbons
React with oxygen
React with NO
Flue gas desulfurisation
React with calcium oxide
SO2 + CaO -> CaSO3
React with calcium carbonate
SO2 + CaO3 -> CaSO3 + CO2
