Organic chemistry pt 1 ( intro to organic, alkanes, intro to halogenalkanes) Flashcards
Define hydrocarbon
a compound consisting of hydrogen and carbon only
Define unsaturated hydrocarbon
contain a c=c bond in hydrocarbon
Define molecular formula
the formula which shows the actual number of each type of atom
Define saturated hydrocarbon
contain single carbon-carbon bonds only
State what is meant by the term structural isomers
molecules with the same molecular formula but with different structural formulae
What is the formula for the ring alkanes and why
CnH2n = because the end hydrogens aren’t needed
Describe the three types of structural isomerism
Positional = functional group is attached to the main chain at different points
Functional = there are different functional groups
Chain = the hydrocarbon chain is arranged differently
What is the general functional group for aldehydes?
What is it converted to in functional group isomerism and what is the general functional group of this isomerism?
What is the general functional group for carboxylic ?
What is it converted to in functional group isomerism and what is the general functional group of this isomerism?
ester
the top one is ester
What is the general formula for alkanes and alkenes?
Alkanes = CnH2n+2
Alkenes= CnH2n
What is the chemical formula for the prefixes methyl, ethyl, propyl, and butyl?
methyl = CH3
ethyl= C2H5
propyl= C3H7
butyl= C4H9
Define displayed formula
show all the covalent bonds and atoms presents in a molecule
Define empirical formula
shows the simplest whole-number ratio of atoms of each element in the compound
Describe and explain the physical properties of alkanes
- non-polar = Carbon and Hydrogen have similar electronegativities = only have van der waals
- short-chained = low boiling points = less electrons, so less van der waals, which makes it collectively weak
- branched = low boiling points than straight = cannot pack together as closely as unbranched chains so van der waals are not as effective
- insoluble = water molecules are polar and have hydrogen bonds which are much stronger. Alkenes are unable to break or weaken these bonds, to form bonds with oxygen and hydrogen atoms
- soluble in non-polar solvents
- unreactive towards acids, alkalis, oxidizing/reducing agents, but may react with halogens under certain conditions
What is crude oil?
It is a mixture mostly of alkanes and hydrocarbons, both unbranched and branched.
Fossil fuel.
How is crude oil formed?
formed from the decay of sea creatures over millions of years
How is fractional distillation carried out?
- Crude oil is first heated in a furnace
- A mixture of liquid and vapour passes into a tower that os cooler at the top than at the bottom
- The vapour pass up the tower via a series of trays containing bubble caps until they arrive at the tray that is sufficiently cool (lower than their boiling point). Then they condense to liquid
- The mixture of liquids that condenses on each tray is piped off
- The shorter chain hydrocarbons condense in the trays nearer to the top of the tower, where it is cooler.
Why does fractional distillation work?
Because crude oil is a mixture of hydrocarbons with different lengths= different boiling points = will separate at different fractions
Why do longer hydrocarbon have a higher boiling point
stronger inter molecular forces
Fractions (highest to lowest)
Liquid petroleum gas, petrol, Naphtha, Kerosene, Diesel, Mineral oil (lubricating), fuel oil, wax, bitumen
What is the basic principle of Cracking?
Longer chain fractions being broken into shorter lengths
Explain the main economic reason why alkanes are cracked.
To produce substances which are (more) in demand / produce products with a high value / products worth more
*
What is the reason for cracking?
shorter hydrocarbons are more useful and economically more valuable
What are the uses of alkenes
useful as chemical feedstock (supply industries with the starting materials to make different products)
can be converted into polymers, and also paints and rugs
What’s the deal about thermal cracking? (3)
include how the carbon-carbon bonds break
- Takes place at high temperatures ( up to 1000 degrees Celsius) and high pressures
- Produces alkenes
- Carbon-carbon bonds break in such a way that one electron from the pair in the covalent bond goes to each caron atom= two shorter chains are produced with free radicals = to stabilize itself, it breaks off a C-H bond removing a hydrogen=not enough hydrogen atoms to produce two alkanes, one of the new chains must have double carbon bond producing an alkene
Why are alkanes only shortly exposed to high temperatures in thermal cracking?
to avoid decompositions
The carbon-carbon bonds break via what process?
homolytic bond fission (thermal cracking)
How are alkenes of a low MR created in thermal cracking and why?
because the chain breaks closer to the end at high temperatures = shorter chained alkenes
What are the intermediates involved in thermal cracking?
free radicals
Why are branched alkanes more useful as motor fuels
because they burn more uniformily
What’s the deal with catalytic cracking? (5)
ph? intermediates?
- takes place at high temperatures and moderate pressure
- uses zeolite catalyst, which has a honeycomb structure = LSA
- acidic
- produces mostly branched alkanes, cycloalkanes, and aromatic hydrocarbons
- intermediates involved are carbocations (carbonium ions)
Why do branched alkanes have a lower boiling point
less closely packed together
weaker van der waals been molecules
less surface contact between molecules
Which produces a higher proportion of alkenes, thermal cracking or catalytic cracking?
thermal cracking
What is a free radical?
A carbon atom with an unpaired electron. Highly reactive intermediates.
State why a high temperature is needed for cracking reactions to occur
you need a lot of energy to break the strong carbon-carbon covalent bonds
State the pros and cons of thermal cracking?
pros:
- a lot of alkenes formed = useful to make polymers (plastics)
- All long-chain hydrocarbons can be thermally cracked even those in the residue
Cons:
- High temperature and pressure mean high energy costs
- complete decomposition can occur at very high temperatures
State the pros and cons of catalytic cracking?
Pros:
- branched-chain alkanes burn more smoothly and so make better fuels
- use of catalyst reduces energy costs
- temperature is lower so complete decomposition avoided
Cons:
- Hydrocarbons must be in the gas phase so very long-chain hydrocarbons cannot be cracked catalytically
In a plentiful supply of oxygen, what are the products of the combustion of alkanes?
co2 and water
What are the products of incomplete combustion of alkanes?
CO and/or C and water
What are the pollutants produced by hydrocarbon-based fuels derived from crude oil, and why are they dangerous?
- CO (carbon monoxide) - poisonous
- Nitrogen oxides - may react with water vapour and oxygen in the air to form nitric acid = acid rain and photochemical smog
- Sulfur dioxide = contributes to acid rain by combining with water capour and oxygen in the air to form sulfuric aci
- particulates (carbon particles) =exacerbate asthma and cause cancer
- unburnt hydrocarbons = contribute to photochemical smog = variety of health problems
- CO2 = greenhouse gases
- water vapour = green house gas
How are nitrogen oxides formed?
produce in petrol engines = due to the high temperatures, it is able to break the strong N=N bonds = nitrogen reacts with oxygen
How is photochemical smog made?
oxides of nitrogen react with unburnt hydrocarbons in the presence of sunlight
Why is acid rain bad?
because it kills aquatic life, damages (limestone) buildings,plants and trees
Write the chemical equation to how sulfuric acid is formed
What is the process of removing sulfur dioxide gas from flue gas (the gas that comes out of power stations
flue gas desulfurisation
How is sulfur dioxide gas removed from flue gas
Calcium oxide ( a base, usually limestone) is used to neutralize the acid gas emissions, forming calcium sulfite
The calcium sulphite is then oxidized in air to form calcium sulphate (gypsum)
co2 is released
Describe how pollutants are removed using a catalytic converter?
- Gases are passed through a ceramic honeycomb structure coated in precious metals (e.g. platinum, rhodium and palladium)
- honeycomb shape = enormous surface area, with minimal use of the metal = saves cost
- polluting gases pass over the convertor, forming less harmful gases
- CO + NO → CO2 +1/2 N2
- the unburnt hydrocarbons + nitrogen monoxide = Nitogren + CO2 +H2O
Describe the greenhouse effect?
UV and visible radiation from the sun is absorbed by the earth and then emitted at much longer wavelengths as infra-red radiation. This radiation is then absorbed by greenhouse gases in the atmosphere which traps the energy and so prevents it from escaping.
What do greenhouse gases include?
Greenhouse gases include CO2, water vapour, methane and surface ozone
What are the properties of halogenoalkanes?
- insoluble = only contain dipole-dipole attractions and van der waal forces ( not polar enough to attract water)
- The boiling point increases with increased chain length and has you go down group 7 = increased van der Waal forces because the larger the molecules, the greater the number of electrons (and therefore the larger the van der Waals forces)
Why do halogenoalkanes have higher boiling points than alkanes with similar chain lengths
because they have higher relative molecular masses and they are more polar
What is the most reactive halogenoalkane and what is the least reactive halogenoalkane?
iodo-compounds are the most reactive and fluro-compounds are the least reactive. This is because as you go down group 7, the molecular mass of the halogen atom increases, the attraction of the electrons to the nucleus gets weaker, so the bond enthalpies fall.
this means C-I would be a weak bond = more reactive
what is the functional isomerism of an alkene
a cycloalkane
What is the functional group for alcohol
What is it converted to in functional group isomerism and what is the general functional group of this isomerism?
ether
left one alcohol
What are the features of a homologous series?
show a gradation/trend/gradual change in physical properties/ a specified property
differ by CH2
chemically similar or react in the same way
have the same functional group
general formula
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