Alkanes Flashcards
What is the general formula for an alkane?
CnH2n+2
State the mixtures from top to bottom in order
Refinery Gases don't condense Gasoline Naptha Kerosene Diesel oil Fuel oil Residue (long hydrocarbons)
How does fractional distillation work?
The vaporised oil enters the column in which there’s a temp. gradient. Cooler at the top. At the top, low viscosity, more flammable due to a low activation energy.
Explain how global warming arises
Burning fossil fuels produces CO2 (greenhouse gas). CO2 absorbs infra red radiation (heat) from sun but emits some back onto earth (greenhouse gas effect). Increasing amount of CO2 - increasing global temps - Global Warming
How does Carbon Monoxide form and state it’s effect
This is formed via Incomplete Combustion which Is poisonous to humans and contributes to the greenhouse effect
How do unburnt hydrocarbons form and state the effects
They are formed when the engine is no hot enough or inefficient and irritate the lungs and react photochemically with sunlight to produce smog
How do Oxides of Nitrogen form and state the effects of them
Formed by N2 + O2 –> 2NO at high temperatures in engines. It can combine with water to produce nitric acid; component of acid rain or contribute to photochemical smog
What are catalytic converters?
They can remove the pollutants (Carbon Monoxide, Unburnt Hydrocarbons, Oxides of Nitrogen). They have a honey comb structure and is coated with a thin layer of platinum; increasing surface area.
Why is cracking useful?
This is when we crack heavier fractions into smaller, more useful ones and there is a demand for smaller ones
Explain the conditions of Thermal Cracking and the products?
High temperatures (900°C) 700kPa Steam Homolytic Products are alkenes which can be used as chemical feedstock and conversion to polymers (plastics)
Explain the conditions of Catalytic Cracking and the products
High temperatures (450°C) Slight pressure Zeolite catalyst to lower temp needed Heterolytic Products are branched alkanes, cycloalkanes
Explain how Flue Gas Desulphurisers works
In the first step, forms Calcium Sulphite
SO2 + CaO –> CaSO3
It is then oxidised by oxygen into Calcium Sulphate (gypsum and is used as plaster)
CaSO3 + 1/2O2 –> CaSO4
Explain what Sulphur - containing impurities can lead to
Fossil fuels contain Sulphur impurities, when the file burns, Sulphur is combusted to form Sulphur dioxide.
S + O2 –> SO2
The gas reacts with water to form sulphurous acid
SO2 + H2O –> H2SO3
What distinguishes whether an elimination reaction happens or substitution
alkene will form if ethanol used as solvent or alcohol if water is used as the source of OH ions
What is produced from catalytic cracking?
|> Aromatic Rings (e.g. Benzene)
Motor Fuels
Aromatic Hydrocarbons
Define: Initiation (free-radicals)
Formation of radicals under UV light
What does Thermal Cracking produce?
|> Alkanes
|> High % of Alkenes
What are the Catalysts used in Catalytic Converters?
Rh, Pd, Pt
Why does boiling point decrease as no. of branches increases?
|> Less points of contact
|> VDWs become weaker
|> Less energy to break
Why are Alkanes not soluble in Water?
|> They are non-polar
|> Water molecules are held together by hydrogen bonds, which are much stronger than VDW
Define: Structural isomers
Molecules with the same molecular formula but a different structural formula
Define: Chain isomers
Same molecular formula, different longest chain lengths with -yl groups
Why do catalytic converters have a honeycomb structure?
Larger Surface Area
What do Catalytic Converters remove?
CO, NOₓ & unburnt hydrocarbons
How are Nitrogen Oxides (NOₓ) produced?
N₂ + O₂ & electrical spark
What causes photochemical smog?
Ozone (O3) and Solid Carbon particulates mixing
What 3 things react together to form ozone?
Sunlight
Hydrocarbons
Nitrogen Dioxide
What are the effects of photochemical smog?
Harm respiratory system in animals and damages plants
