6.2 - alkanes & alkenes Flashcards
what is the general formula of alkanes?
CnH2n+2
which 2 types of hydrocarbons are saturated?
alkanes & cycloalkanes
which 3 ways are alkane fuels obtained from?
fractional distillation, cracking, reforming of crude oil
what does reforming do?
convert straight-chained hydrocarbons into branched / cyclic for efficient combustion
how does fractional distillation work?
- crude oil heated in a furnace & flows into fractioning tower
- vapour passes up and condenses at different regions
in which direction does the fractioning column get cooler? what hydrocarbons are harvested there?
upwards, hydrocarbons with low chain length / boiling point
what are the products of complete combustion of alkanes?
CO2 + H2O
what are the products of incomplete combustion?
CO + H2O
why is CO toxic to the human body?
binds to haemoglobin, less O2 transported
what other pollutants are produced during combustion? what are their impacts?
- nitrogen oxides -> reacts with oxygen & forms acid rain
- sulfur oxides -> acid rain & damages catalytic converters
- carbon particulates -> coughing (heart disease & lung cancer)
what are some examples of alternative fuels from renewable sources?
- alcohols
- biodiesel
what is an radical?
species with unpaired e-
describe the 3 steps of free-radical substitution with halogens.
1) initiation
- produces free radical from molecules
2) propagation
- forms products & more radicals
3) termination
- removes free radicals
under what conditions does alkanes react with halogens?
under UV light / on heat
what are the limitations of using free-radical substitution?
- mixture of products
- further substitution products
what is the general formula of alkenes?
CnH2n
what types of organic molecules have the general formula of CnH2n?
alkenes & cycloalkanes
when does e/z isomerism occur?
when there is restricted rotation about a bond with 2 different groups attached
which type of hydrocarbon produces a cleaner flame when combusted?
alkanes
what reaction conditions are involved in the electrophilic addition of H2 to alkenes? what is the product?
Ni catalyst, 150C, 5 atm
forms alkanes
what reaction conditions are involved in the electrophilic addition of steam to alkenes? what is the product?
conc. H3PO4 catalyst, 300-600C, 70 atm
produce alcohols
what reaction conditions are involved in the oxidation of alkenes? what is the product?
acidified KMnO4 + steam
produce diols
what will be the colour change observed when alkenes are oxidised by potassium manganate?
pink -> colourless
