Topic 10- Alkanes Flashcards
What is the general formula for alkanes?
What is the general formula for alcohols?
What are alkanes a member of?
What are alkanes referred to and why (in full detail)?
How are the bonds spaced in alkanes?
What is the first examples of structural isomerism in alkanes?
What is the boiling point like as alkanes increase in size?
What does more atoms result in?
What does greater intermolecular force require?
What does greater energy required result in?
Cn H2n +2
Cn H2n +2 O
A homologous series
Saturated hydrocarbons- all carbon-carbon bonding is single
The bonds are spaced tetrahedrally about carbon atoms
First example of structural isomerism occurs with C4H10 (butane)
Boiling point increases as they get more carbon atoms in their formula
More atoms= greater intermolecular Van der Waals’ forces
More energy to separate the molecules
Higher boiling point.
Why does the difference in boiling point get less as the size of alkanes increases?
What must be written in an exam about Van der Waals forces?
What do straighter chain molecules have that’s better than branched?
What does the greater the branching result in?
What happens to melting point in alkanes?
What is this trend not as regular for?
What are alkanes, concerning polarisation?
What are they soluble in most?
Mass increases by a smaller percentage
Must write Van der Waals forces between molecules
Straighter chain molecules have greater interaction than branched
The greater the branching, the lower the boiling point
Melting point generally increases with molecular mass
Not as regular as that for boiling points
Non-polar so are immiscible with water (ie don’t dissolve in water)
Alkanes are soluble in most organic solvents.
What is the reactivity of alkanes like?
What are the bonds like of alkanes?
What don’t alkanes have on their structures?
What do alkanes make as useful reactants?
How do alkanes react with oxygen?
What does the greater the number of carbon atoms result in?
But does this then also require?
What is a handy tip for when balancing equations involving complete combustion (in full)?
Fairly unreactive
Have relatively strong, almost non-polar, single covalent bonds
They have no real sites that will encourage substances to attack them
Make useful fuels- especially lower members of the series
React with oxygen in an exothermic reaction
More energy produced
The greater the amount of oxygen needed for complete combustion
Every carbon in the original hydrocarbon gives one carbon dioxide and every two hydrogen atoms gives a water molecule.
Why does fractional distillation work?
What does longer chain hydrocarbons have?
What does industrial cracking involve?
What does industrial cracking convert?
What does thermal cracking proceed via?
What does catalytic cracking proceed via?
What is the pressure and temperature like of thermal cracking?
What are the two other properties of thermal cracking?
What does thermal cracking mostly produce?
What else does thermal cracking produce and what two processes is this then used in?
By what two processes can bonds be broken anywhere in the molecule?
Because the different substances in the mixture have different boiling points
Longer chain hydrocarbons have higher boiling points
The breaking of C-C bonds in alkanes
Long chain molecules into higher value products
A free radical mechanism
A carboncation (carbonium ion) mechanism
High pressure: 7000 KPa ; high temperature: 400 oC to 900 oC
Free radical mechanism and homolytic fission
Produces mostly alkenes (eg ethene for making polymers and ethanol)
Produces hydrogen… used in the Haber Process and in margarine manufacture
C-C bond fission or C-H bond fission.
What is the pressure and temperature of catalytic cracking like?
What type of catalyst is used?
What are two other properties of catalytic cracking?
What three things does catalytic cracking produce?
What are the products of catalytic cracking used for?
What are zeolites?
Slight pressure ; high temperature: 450 oC
Zeolite catalyst
Carboncation (ionic) mechanism and heterolytic fission
Produces branched and cyclic alkanes, aromatic hydrocarbons
Motor fuels
Zeolites are crystalline aluminosilicates; clay like substances
Describe fully what happens to shorter chain alkanes in complete combustion?
What are these combustion reactions described as and why?
What do they have concerning enthalpy?
What happens the more carbons present in an alkane?
What is useful about these properties of alkanes for us?
What are fuels?
What do fuels also do?
What happens to alkanes in a limited supply of oxygen?
What does this reaction produce?
What is produced if there’s even less oxygen present?
What can be used when balancing diatomic gases?
The shorter chain alkanes burn completely in a plentiful supply of oxygen to give carbon dioxide and water
Exothermic because they give out heat
They have a large negative enthalpy of combustion
The greater the heat output
Important to us as fuels
Substances that release heat energy when they undergo combustion
Fuels also store a large amount of energy for a small amount of weight
They burn in incomplete combustion
The poisonous gas carbon monoxide, CO
Carbon (soot) is produced
Half of a compound can be used.
Describe the following by products/products of the combustion of alkanes (in full detail):
Carbon Monoxide
Nitrogen Oxides
Sulphur Dioxides
Carbon Particles
Unburnt Hydrocarbons
Carbon Dioxide
Water Vapour
What two things do sulphur oxides combine with and what does this form?
What two things are nitrogen oxides contributors to?
CO, a poisonous gas produced by incomplete combustion
Abbreviation NOx, produced when there is enough energy for N2 and O2 in the air to combine
Another contributor to acid rain. Produced in sulphur-containing impurities present in crude oil
Called Particulates. Can exacerbate (make worse) asthma and cause cancer
May also enter the atmosphere and these are significant greenhouse gases. Contributes to photochemical smog which can cause a variety of health problems
A greenhouse gas. Always produced when hydrocarbons are burnt. Although CO2 is necessary, increasing rise in atmosphere which could be a contributing factor to climate change and global warming
Also a greenhouse gas
Combine with water vapour and oxygen in the air to form sulphuric acid
Acid rain and photochemical smog.
What do power stations cause concerning pollution?
What three things do internal combustion engines produce?
What does effluent mean?
How is SO2 removed?
How are CO and NOx removed?
What happens to the following in a catalytic converter:
CO
NOx
Unburnt Hydrocarbons
What three metals are catalysts made from?
What two things does leaded petrol do to catalytic converters if it passes through it?
SO2 emissions which produce acid rain
CO, NOx and unburnt hydrocarbons]
Waste (either liquid/gas)
React effluent gases with a suitable compound (eg CaO)
Pass exhaust gases through a catalytic converter
CO is converted to CO2
NOx is converted to N2
Unburnt hydrocarbons are converted to CO2 and H2O
Finely divided rare metals Rh, Pd and Pt
- Lead deposits on the catalysts surface and poisons it
- Thus blocking sites for reactions to take place.
Why is water not a problem as a greenhouse gas?
What are unburnt hydrocarbons and give an example?
What does carbon dioxide do in the Earth’s atmosphere and what is the result?
What does visible radiation do to the atmosphere and what does this cause?
What is emitted by the Earth and what does this do?
What is some of this trapped by and why?
Because the amount in the atmosphere stays roughly constant
Potent greenhouse gases (methane from animals is a problem)
Carbon dioxide traps infra-red radiation so that the Earth’s atmosphere heats up
Visible radiation (sunlight) readily penetrates the atmosphere and warms the Earth
Invisible infra-red radiation is emitted by the Earth and cools it down
Some of this infra-red radiation is trapped by greenhouse gases in the atmosphere, keeping the heat in.
