alkanes [O1] PAPER 2 Flashcards
what is the general formula of an alkane?
Cn H2n+2
what are the conditions and main products of thermal cracking?
• high temperature
• high pressure
• C-C bonds are broken
• mainly alkenes
what are the conditions and main products of catalytic cracking?
• high temperature
• slight pressure
• zeolite catalyst
• C-C bonds are broken
• mainly branched alkanes and aromatics
why does boiling point increase as the chain length of an alkane increases?
• surface area increases
• molecules are packed closer together
• stronger van der Waals’ forces between molecules
why are high temperatures needed for cracking?
break (C-C / C-H) bonds
cracking equations - what must you ensure? (when filling blanks)
total number of Cs and Hs in products add up to the molecule on the left side of the arrow
define hydrocarbon
contains ONLY hydrogen and carbon
what is meant by a saturated hydrocarbon?
single bonds only
OR no double bonds
what is meant by an unsaturated hydrocarbon?
C=C/carbon double bonds present
why should sulfur compounds found in crude oil be removed from fractions before they are used for fuels?
• (when combustion occurs) sulfur dioxide is produced
• sulfur dioxide causes acid rain
state the physical property that allows compounds to be separated by fractional distillation
different boiling points
Outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions
• compounds have different boiling points and separate depending on their boiling points
• these boiling points depend on the size of the compounds
• temperature gradient in column (cooler at top of column/hotter at the bottom of the column)
• Larger molecules at bottom of column
explain how oxides of nitrogen may be produced during the combustion of paraffin in air
nitrogen and oxygen from air react with each other at high temperatures
write an equation to show how nitrogen monoxide in the air is converted to nitrogen dioxide
2NO + O2 -> 2NO2
why is the melting point of a molecule made up of a long carbon chain higher than a molecule made up of a short carbon chain?
• larger molecule so has a larger surface area and molecules are packed closer together
• stronger van der Waal’s forces between molecules
what are the hazards of soot (solid carbon)?
• causes global dimming
• causes breathing problems
• smog
• makes visibility poor
• exacerbates asthma
Explain the main economic reason why alkanes are cracked
to produce substances (shorter chain molecules) that are in higher demand
[e.g. short chain hydrocarbons needed for fuel]
identify a catalyst used in catalytic converters
iridium / platinum / palladium / rhodium
why do the products of complete combustion result in environmental problems?
CO2 and H2O evolved are greenhouse gases / contribute to global warming
equations for the combustion of alkanes to produce (1) incomplete combustion to produce a solid, (2) incomplete combustion to produce a gas and (3) complete combustion
(1) alkane + O2 (g) -> C (s) + H2O (g)
(2) alkane + O2 (g) -> CO (g) + H2O (g)
(3) alkane + O2 (g) -> CO2 (g) + H2O (g)
why is carbon monoxide harmful?
it is toxic / poisonous
Identify a compound that is used to react with the sulfur dioxide in the products of combustion before they enter the atmosphere.
Give one reason why this compound reacts with sulfur dioxide.
Suggest the name of the process that occurs when this reaction takes place.
• calcium oxide / calcium carbonate
• it is a base / neutralises the sulfur dioxide / acid base reaction
• neutralisation
what raw material are hydrocarbons obtained from and how can they be separated out?
• crude oil
• fractional distillation
A catalytic converter is used to remove carbon monoxide from the exhaust gases in a car.
Write an equation to show how carbon monoxide is removed in a catalytic converter.
2NO + 2CO → N2 + 2CO2
