Alkanes and halogenoalkanes Flashcards
(27 cards)
State the general formula of alkanes
CnH2n+2
Where are alkanes found?
In crude oil, which is a mixture of different lengths of hydrocarbons
Describe the process of fractional distillation
- Crude oil is vaporised using a furnace to about 350°C
- The column has a temperature gradient, it is cooler at the top. This means that as the vapour rises parts of the mixture condense at different temperatures.
* This is because there are different chain lengths and hence different boiling points. - The vaporised oil then enters the fractional column and rises through the trays - the longest hydrocarbons don’t vaporise and run down to the bottom.
- The fractions are drawn off at different levels.
What is cracking and what can it be used for?
Cracking is breaking longer chain alkanes into shorter chain hydrocarbons. It can be used to crack heavier fractions into higher demand, lighter fractions.
What does cracking produce?
An alkane and an alkene.
What are the two types of cracking?
- Thermal cracking
- Catalytic cracking
What are the conditions for thermal cracking?
High temperature and pressure
1000 °C and 70 atm of pressure
What are the products of thermal cracking and what can they be used for?
Alkenes and they can be used to make polymers e.g plastics.
What are the conditions for catalytic cracking?
High pressure and slight pressure
450°C and a zeolite catalyst
Why is a zeolite catalyst used in catalytic cracking?
It lowers the temperature and pressure needed for cracking to occur - this lowers costs and speeds up the process.
What are the products of catalytic cracking and what are they used for?
Aromatic hydrocarbons that are used in fuels for vehicles.
What role does carbon dioxide play in the greenhouse effect?
Burning fossil fuels (crude oil) can release carbon dioxide which absorbs infra-red radiation (heat) from the sun but emits some of it back into the earth which is called the greenhouse effect.
What is ozone?
The lowest layer of the atmosphere which exists as sunlight, hydrocarbons and nitrogen dioxide. Cars and some factories also produce hydrocarbons and nitrogen dioxide.
What happens when the ozone mixes with solid carbon particulates?
Photo-chemical smog is created - this can harm the respiratory system in animals and harms plants.
How can burning fossil fuels produce sulfur dioxide?
Some fossil fuels contain sulfur based impurities, when they react with oxygen this produces sulfur dioxide.
What happens when sulfur dioxide reacts with water?
Sulfur dioxide is an acidic gas and when it reacts with water in the atmosphere this can form sulfuric acid which falls as acid rain.
What does acid rain do?
Damages plants, kills fish and causes building to erode.
How can we remove sulfur dioxide from flue gases?
Wet scrubbing - this involves dissolving calcium carbonate/oxide in water and spraying it on the acidic sulfur dioxide gas.
How do boiling points of halogenoalkanes change down the group and why?
Boiling points of halogenoalkanes increase down the group because there are more electrons which means more van der waals forces between molecules - more energy is needed to overcomes these forces.
What is a nucleophile?
Electron pair donor
What is an electrophile?
Electron pair acceptor
What are CFCs and what do they do?
CFCs are chlorofluorocarbons that have had all of their hydrogens replaces by chlorine and fluorine. They were used as refrigerants and propellants in deodorants.
How are CFCs broken down?
C-Cl bonds are broken down by UV radiation in the atmosphere, radicals are formed which catalyse the break down of the ozone.
**MAKE SURE TO BREAK C-CL SINCE THEY HAVE THE LOWEST BOND ENTHALPY
Why are CFCs banned?
They break down the ozone layers which is important as the ozone absorbs harmful UV radiation that causes skin cancer.
