alkanes Flashcards
what is a biofule
a fule produced from renewable biological resources
what does it mean if something is carbon neutral
an activity that has no net carbon dioxide emmisions to the atmosphere
what is a catalyst
a subatance that speeds up a chemical reaction but remains unchanged at the end
what is a fraction
a group of hydrocrbons with similar boiling points
what is a free radical
species with an unpaired electron
what is a homologus series
a family of compounds with the same general formula and similar chemical properties. Each member differs by the addition of CH2 and there is a gradual change in physical properties
what is a molecular formula
formula that gives the actual number of atoms of each element in one molecule
what trend do the boiling points of alkanes follow and why
as the carbon chain gets longer, the bp increases. This is because electrons are increased, increasing van der waals forces.
why do straight chain alkanes have stronger van der waals forces than branched chained
van der waals forces are strongest when molecules have lots of suface contact. Branches on the chain disrupt contact
what are van der waals forces
Electrons are free to move and this causes instantaneous negative dipoles. this induces a positive dipole in another molecule. The two are attracted by the electrostatic force known as van der waals
what is cracking
when long chain molecules are broken down into more useful smaller molecules. An alkene is always a product.
what conditions does catalytic cracking require?
pressure slightly above atmospheric and temperature of 450 degrees.
what kind of catalyst does cracking use
a zeolyte catalyst. (a form of aluminosillicate)
what products does catalytic cracking give you?
branched and cyclic hydrocarbons, aka aromatic hydrocarbons.
what conditions does thermal cracking require
high pressure and temperature
what products does thermal cracking give you
straight chain alkanes used for polymers
whats good about zeolyte catalysts
they are pourous and have large surface areas
what is the equation for complete combustion of alkanes
alkane + oxygen = carbon dioxide + water
what does incomplete combustion produce
soot or carbon monoxide and water
why are unburnt hydrocarbons a pollutant and what is a possible solution
they pass through engines unburnt. They are carconogenic and act as greenhouse gases. solutions include catalytic converters and careful mixing of fule
what is carbon monoxide
a colourless, odourless toxic gas that binds with haemoglobin preventing gas exchange.
what is soot. why is it bad
small particulates of carbon
dangerous if eneters lungs, blocks engine parts, contributes to global dimming
why are oxides of nitrogen pollutants? what is the solution?
reacts with water to form acid rain. solutions include catalytic converters
how are NOx formed
high temps in engine cause N2 from air to react with oxygen
how do catalytic converters work
a ceramic honeycomb covered in a thin layer of catalyst metals (Pt, Pd, Rh) which gasses pass through
what are the equations for the catalytic converter
removing CO and NO: 2CO + 2NO = 2CO2 + N2
removing unburnt hydrocarbons: hydrocarbon + NO = CO2 + N2 + H2O
how is sulfur dioxide formed
fules contain sulfur and during combustion SO2 is formed
how is sulfur dioxide a pollutant and what are the solutions
it reacts with water to form acid rain. it’s toxic and can cause repiratory problems. solutions include flue gas desulfurisation
how does flue gas desulfurisation work
waste gas or fule passes through a scrubber. The scrubber is calcium oxide or calcium carbonate. an acid base reaction occurs removing the sulfur
what is the equation for flue gas desulfurisation
CaO + SO2 = CaSO3
OR
CaCO3+ SO2= CaSO3+CO2
calcuim sulfate is also known as gypsum and it can be used to make plasterbord.
how does fractional distilation work
crude oil is vapourised. vapour is passed through a tower with a temp gradient (cool at bottom hot at top). As it rises, it cools. Molecules condence at different hights as they have different boiling points. Longer chains have higher boiling points.
what is the greenhouse effect?
greenhouse gasses absorb and emmit infared radiation. IR radation excites the bonds in the gasses causing them to vibrate more vigourously. Molecules then re emmit the energy in all directions as heat, heating up the atmosphere
what is carbon footprint
a measure of the impact our activities have on the environment in terms of amount of greenhouse gasses produced. Measured in untits of carbon dioxide
what is the overall equation of a free radical substatution mechanism
alkane + halogen = halagenoalkane + hytogen halide
what is the initation stage of free radical substitution
halogen = halogen free radical
e.g Cl2 = 2Cl free radicals
what are the propagation steps of free radical substitution
radical + molecule = radical of molecule + hytrogen halide
radical of molecule + halogen molecule =product + halogen free radical
what is the termination steps of free radical substution
any step that does not produce free radicals. (two radicals reacting together)
what is ozone
an allotrope of oxygen formula O3
what is the ozone layer
a layer that absorbs most of UV radiation
equation for ozone formation
O2= two O free radicals, each with two unpaired electrons
O2 + O free radical = O3
equation for ozone depletion
O3 = oxygen free radical + O2
