alkanes Flashcards
(31 cards)
what are alkenes
Alkenes are unsaturated hydrocarbons meaning they contain a carbon-carbon double bond
what does saturated mean
Compounds contain single bonds only
what is the general formula for an alkane
CnH2n+2
why does the boiling point of alkanes increases with increasing C chain length
· Alkanes have induced dipole-dipole attractions between molecules
· Strength of attractions increases with increasing size of molecule and number of electrons
· The longer the C chain, the bigger the molecule and the more electrons
2,2-dimethyl propane and pentane both have the same number of electrons, but pentane has a higher boiling point. This is because:
· 2,2-dimethyl propane has more branches than pentane
· There is more surface contact between molecules of pentane than molecules of 2,2-dimethyl butane
· The induced dipole-dipole attractions between molecules of pentane are stronger
what is a fraction
A mixture of compounds with similar boiling points and similar sized molecules
what is crude oil
Crude oil is a mixture of hydrocarbons with different chain lengths
what is fractional distillation used for
Fractional distillation is used to separate hydrocarbons based on their differing boiling points, which is determined by their C chain length
describe how crude oil is separated into fractions using fractional distillation
· Crude oil is heated to vapourise it so everything is at a gaseous state and enters the column
· Hydrocarbons have different boiling points
· Boiling point depends on size/Mr/chain length
· The column is cooler at top and hotter at the bottom (temp gradient)
· Larger molecules with higher boiling points condense at the bottom
why is cracking used
breaks the larger fractions (for which supply exceeds demand) into smaller fractions (for which demand exceeds supply and also makes alkenes
what does thermal cracking produce
always produces one alkane, with all other molecules being alkenes
what does catalytic cracking produce
high percentage of branched alkanes and cycloalkanes.
what are the conditions for thermal cracking
high temperatures and high pressures
what are the conditions for catalytic cracking
high temperatures
slight pressures
a catalyst - zeolite crystal
what are the conditions for complete combustion
plentiful supply of oxygen
give a equation for complete combustion of nonane
C9H20 + 14O2 → 9CO2 + 10H2O
give 2 possible products of incomplete combustion
carbon monoxide gas or solid carbon (soot) + water
state chemicals are produced during combustion and give their polluting effect
CO2 Greenhouse gas
H2O Greenhouse gas
CO Poisonous
Solid C Damages the lungs/ exacerbates asthma
give the equation for how sulfur dioxide is formed when Sulphur impurities are burnt
S(s) + O2(g) →SO2(g)
give the equation for the formation of acid rain (from Sulphur impurities)
SO2(g) + 0.5 O2(g) + H2O(l) → H2SO4(l)
what gas dissolves in rainwater form acid rain
SO2 (or HNO3)
how are oxides of nitrogen formed
the high temperatures in the car engines cause some of the nitrogen to react with the oxygen to produce oxides of nitrogen
give the equation for the formation of acid rain (from nitrogen dioxide)
4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(g)
some unburnt hydrocarbons are toxic if breathed in give an example
C8H18
