topic 6b: alkanes Flashcards
1
Q
general formula alkane
A
CnH2n+2
2
Q
what is an alkane?
A
saturated hydrocarbon
3
Q
alkane main use
A
fuels
4
Q
how do u obtain alkane fuels
A
fractional distillation , cracking, then reforming of crude oil
5
Q
how does fractional distillation work
A
- oil heated and passed into column
- temperature of column DECREASES upwards
- fractions condense at different heights according to boiling point
- bp depends on size of molecule
- larger molecule = stronger LF so higher boiling point
- molecules of similar length condense together
- small molecules condense at the low temps at the top
- bigger molecules condense at high temps at the bottom
6
Q
cracking
A
conversion of large hydrocarbons to smaller molecules by breakage of C-C bonds
7
Q
reasons for cracking?
A
- shorter C chains in higher demand than longer
- more useful- eg alkenes used to make polymers. smaller alkanes for motor fuels (burn more efficiently)
8
Q
reforming
A
processing of straight-chain hydrocarbons into
branched-chain alkanes and cyclic hydrocarbons for efficient combustion
9
Q
purpose of reforming
A
- branched and cyclic hydrocarbons burn more cleanly
- give fuels a higher octane number
10
Q
what is a fuel
A
releases heat energy when burnt
11
Q
why are alkanes good fuels
A
combustion is highly exothermic
12
Q
complete combustion alkane
A
co2+h2o
13
Q
incomplete combustion alkanes
A
- limited amount of oxygen
- less energy per mole produced
- CO(toxic) /C (c gives soot)
14
Q
carbon monoxide
A
- highly toxic
- odourless
- reduces the o2 carrying capacity of blood
15
Q
carbon production problem
A
particulates in atmosphere
