A-LEVEL CHEMISTRY: 3.3.2: Alkanes (ChemRevise) Flashcards
What is ‘Petroleum’?
Petroleum is a Mixture consisting mainly of Alkane Hydrocarbons
What is a ‘Fraction’?
a Fraction is a Mixture of Hydrocarbons with a similar Chain Length & Boiling Point
Explain the process ‘Fractional Distillation Industrially’: (10)
-oil is pre-heated
-then passed into column
-the Fractions Condense at different heights
-the Temperature of the column decreases upwards
-the Separation depends of Boiling Point
-Boiling Point depends on size of Molecules
-the larger the Molecule, the larger the Van der Waals Forces
-similar sized Molecules Condense together
-small Molecules Condense at the top, at lower Temperatures
-big Molecules Condense at the bottom, at higher Temperatures
Cracking:
Conversion of large Hydrocarbon Chains to smaller Hydrocarbon Molecules by breakage of C-C bonds
Economic reasons for Cracking: (3)
-shorter Hydrocarbon Chains are in more demand
-makes use of otherwise useless long Hydrocarbon Chains
-the products of Cracking are more valuable than the starting materials
2 main types of Cracking: (2)
-Thermal
-Catalytic
Thermal Cracking Conditions: (2)
-High Pressure (~7000kPa)
-High Temperature (~400’C - 9000’C)
Products of Thermal Cracking: (2)
-Produces mostly Alkenes
-Sometimes Produces Hydrogen
Thermal Cracking Produces mostly ___.
Alkanes
Thermal Cracking sometimes Produces ___.
Hydrogen
Catalytic Cracking Conditions: (3)
-Slight/moderate Pressure
-High Temperature (~450’C)
-Zeolite Catalyst
Products of Catalytic Cracking: (2)
-Branched Alkanes
-Aromatic Hydrocarbons
Fuel:
Releases Heat Energy when Burnt
Complete Combustion:
in excess Oxygen, Alkanes will Burn with Complete Combustion.
the Products of Complete Combustion are CO2 and H2O
Products of Complete Combustion:
CO2 & H2O
Complete Combustion occurs in…
Excess of Oxygen
Incomplete Combustion:
Limited amount of Oxygen.
Produces CO (v. toxic) and/or C (soot)
Products of Incomplete Combustion: (2)
CO (v. toxic) and/or C (soot)
why are Alkanes used as Fuels?
Alkanes burn in the presence of Oxygen.
this Combustion is highly Exothermic.
SO2 will dissolve in Atmospheric Water, and can Produce:
Acid Rain
how can SO2 be removed from Waster Gas (to prevent acid rain)?
by Flue Gas Desulfurisation
Pollutants from Combustion: (5)
-Nitrogen Oxides
-Carbon Monoxide (CO)
-Carbon Dioxide (CO2)
-Unburnt Hydrocarbons
-Soot (C)
Environmental consequence of the Pollutant ‘Nitrogen Oxides’: (3)
-NO is toxic
-can form NO2 (Acidic Gas)
-Acid Rain
Environmental consequence of the Pollutant ‘Carbon Monoxide’:
toxic
Environmental consequence of the Pollutant ‘Carbon Dioxide’:
contributes towards global warming
Environmental consequence of the Pollutant ‘Unburnt Hydrocarbons’:
contributes towards formation of smog
Environmental consequence of the Pollutant ‘Soot’: (2)
-global dimming
-respiratory problems
Catalytic Converters:
remove CO, Nitrogen Oxides, & Unburned Hydrocarbons from vehicle exhaust gases, turning them into ‘harmless’ CO2, N2 & H2O
Describe Catalytic Converters: (3)
-Ceramic
-Honeycomb
-thin layer of Catalyst Metals (Platinum, Palladium, Rhodium) to give Large Surface Area
Greenhouse Gases: (3)
-Carbon Dioxide (CO2)
-Methane (CH4)
-Water Vapour (H2O)
___ ___ passes through the Atmosphere to the Earth’s Surface and ___ it up.
UV Radiation, Heats
the Earth Radiates out ___ ___ ___ Radiation/
Infrared Long Wavelength
Carbon Dioxide levels have risen significantly in recent years. why?
Increased Burning of Fossil Fuels
In the presence of ___ ___, Alkanes React with Chlorine to form a Mixture of products with the Halogens substituting Hydrogen Atoms.
The Mechanism for this Reaction is:
UV Light, Free Radical Substitution
Steps of Free Radical Substitution: (3)
-Initiation
-Propagation
-Termination
The ___ Light supplies the Energy to break the Cl-Cl bond. This process is called…
UV. Homolytic Fission
Free Radical:
a Reactive species that has an Unpaired Electron
As the Cl Free Radical is generated, it can react with several more Alkane Molecules in a…
Chain Reaction
All Propagation steps have a ___ ___ in the ___ & ___.
Free Radical, Reactants & Products
