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
