Alkanes Flashcards
What is the gen formula of alkanes?
CnH2n+2
Hydrocarbon
compound cont C and H2 only
Saturated
they cont no C=C or C—C bonds
What is the trend with bp in alkanes?
As mol have more C atoms, bp increases
What are the forces of attraction between neighbouring mol in alkanes?
Non-polar and only vdwF
Why does bp increase as chain l increases?
vdwF forces of attr between the mol increases
What happens to bp as branching increases? Why?
The higher the branching in the mol the lower the bp. More branching results in less vdwF between the mol b/c mol cannot pack as close together
What is combustion?
Chem r of fuels with oxygen releasing heat and forming oxides
Whats the trend in relation to hydrocarbons and their ignition?
Hydrocarb bec harder to ignite as mol get bigger b/c bigger mol don’t vaporise so easily
Bigger mol have greater vdw attr which makes it more dif for them to break away from their neighbour and turn into gas
What colour is the flame the bigger the hydrocarbon?
Comb tends to be < complete as no C atoms in mol increases
Bigger the hydr the more likely you are to get a yellow, smoky flame
What colour is flame in compounds with low C?
Blue clean flame
Incomplete Combustion
where there isnt enougb O2 present can lead to form of C or CO
What indicates inc comb?
Sooty flame
What does burning fuels release?
Greenhouse gases
Give e.g of greenhouse gases:
CO2, SO2 AND NO/NO2
How do we reduce air pollution?
Removing s from fuels B4 combustion
Using catalytic converters in cars
Scrubbing emissions (with alkali) from power stations and factories
Using renewable en sources- e.g wind,wave,solar,hydroelectric and tidal
What is the gh effect?
Co2 making up 0.03%-0.04% of atmosphere
What are the conseq of the gh effect?
Climate Change
Raised sea levels
Melting of polar ice caps
What is acid rain?
Acidic gases dissolving into water in env
What is the conseq of acid rain on the env?
Corrosion of limestone features, statues and buildings
Death of fish in lakes and rivers
Defoliation of trees
What do catalytic converters do?
Change poisonous mol like CO and various NOs in car exhausts into more harmless mol like CO2/N2
How are the metals deposited? How does this act as an adaptation?
Metals deposited in thin layers onto a ceramic honeycomb
This max sa and keeps amount of metal used to a min b/c its v expensive
What is catalytic poisoning?
When metal i.e lead coats honeycomb of expensive metals and stops it working
What is the mechanism and conditions for monohalogenation of alkanes?
Free radical photochemical substitution
Under UV light
Inititation R
Molecule -> Radicals
Initation R for CL2
CL2 -> 2Cl’ (dot= radical)
Propagation R
Molecule + Radical -> Radical + Molecule
Write prop r for chlorine and methane:
CH4 + CL’ -> CH3’ + HCl
CH3’ + CL2 -> CH3CL + CL’
Termination R
2 radicals -> Molecule
Write 3 poss term r for chlorine and methane
Cl’ + Cl’ -> CL2
Ch3Cl’ + Cl’ -> Ch3Cl
CH3’ + CH3’ -> C2H6
