Chapter 12- Alkanes Flashcards
What are alkanes?
Saturated hydrocarbons containing only C-C and C-H single bonds.
What is crude oil?
A mixture of hydrocarbons, mostly alkanes, both unbranched and branched. Its fractions can be separated by fractional distillation.
What is the process of fractional distillation?
-Crude oil heated
-Mixture of liquid and vapour passes into fractionating column with temp. gradient
-Vapours rise up the column through trays until they reach a cool enough tray where they condense
-Shorter chain hydrocarbons condense further up due to their lower boiling points
-Thick residue collects at the base (tar/bitumen) which can be processed further or used for road surfacing
What is cracking?
The breaking of longer chain hydrocarbons into shorter chain hydrocarbons through the breaking of C-C bonds
Why are longer chain alkanes cracked?
Longer chain alkanes are in lower demand while shorter chain alkanes and alkenes are in higher demand as they are more useful
Alkenes are more reactive than alkanes and can be used as chemical feedstock
What are the conditions and products of thermal cracking?
-High temperature: 700-1200K
-High pressure: up to 7000 kPa
-Produces mostly alkenes that can be used as chemical feedstock
What are the conditions and products of catalytic cracking?
-Moderately high temperature: 700K
-Moderately high pressure: higher than atmospheric pressure
-Zeolite catalyst (al. oxide and sil. dioxide) in honeycomb structure for high SA
-Produces motor fuels, aromatic compounds (branched alkanes, cycloalkanes) which are separated using fractional distillation
How are alkanes often used?
As fuels, eg methane, propane, petrol, etc.
How can combustion reactions of alkanes differ?
Depending on the amount of oxygen available, combustion can be complete or incomplete and produce different products
Plentiful: carbon dioxide and water
Limited: carbon monoxide and water
Very little: carbon (soot) and water
What are some pollutants that burning crude oil can produce?
CO
NOx
SO2
C
Unburnt hydrocarbons
CO2
H2O
What is carbon monoxide?
CO, a poisonous gas produced by incomplete combustion
What are nitrogen oxides?
NOx, contribute to acid rain and photochemical smog
Produced in petroleum engines at high temp. causing nitrogen and oxygen in the air to combine
What is sulfur dioxide?
SO2, contributes to acid rain
Produced from sulfur-containing impurities in crude oil reacts with water and oxygen to form sulfuric acid
What are carbon particles/particulates?
C, can exacerbate asthma and cause cancer
Produced by incomplete combustion with very little oxygen available.
What are unburnt hydrocarbons and what do they do?
Hydrocarbons
Bad greenhouse gases, photochemical smog
