Alkanes Flashcards
What are the three different types of imf?
- Vdw
- Dipole-dipole forces
- Hydrogen bonds
What are vdw?
Instantaneous dipole
Results in the formation of a very slight negative charge at one end of the atom and the other side has a very slight positive charge where there are less electrons
This cause a very weak attractive force between the delta negative and delta positive of DIFFERENT atoms
These forces exists in all atoms and molecules
What are dipole-dipole forces?
Dipoles in different molecules can interact
This causes an attractive force between different molecules
Some covalent bonds are polar
The arrangement of polar bonds can result in a molecule becoming polar overall
They are permanent
This makes dipole-dipole forces stronger than vdw
When does hydrogen bond form?
With Hydrogen and NOF
Nitrogen
Oxygen
Fluorine
General formula of alkanes
CnH2n+2
How is boiling point affected by carbon chain length?
The longer the carbon chain, the higher the boiling point
Due to stronger vdw forces between molecules
Shorter carbon chain, lower the boiling point
Due to less vdw forces b/w molecules
How does the branches of carbon chains affect boiling point
More branched the carbon chain, the lower the boiling point
Due to weaker vdw forces between molecules
Due to molecule not being packed closely together
Smaller surface area, less energy needed
How is crude oil formed?
Formed by slow decay of marine animals and plants over millions of years under heat and pressure in the absence of air
Consists mainly of alkanes (including cycloalkanes, some aromatics and other compounds containing S and O)
Crude oil has not use in its raw form, so it must be separated
How do you separate the different carbon chains
Fractional distillation
How does fractional distillation work?
- the crude oil is vaporised
- vapour is passed into a tower which is hot at bottom and cold at the top
- the tower has a temp gradient
- As the vapour rises, it cools just before boiling point
- molecules will condense at different heights as they have different boiling points
- the larger the molecule, the lower down the column it will condense
This produces fractions
As the chain gets longer, the hydrocarbons
- become more viscous
- harder to ignite
- less volatile
- higher boiling point
- more vdw
What are fractions?
A mixture of hydrocarbons with similar boiling points
What is the process of turning long carbon chains into shorter ones?
Cracking
Two types of cracking
Thermal
Catalytic
Why is cracking important?
As shorter chains are more in demand and valuable than larger fractions
Thermal cracking conditions
900 degrees c 70 atm (High temp and pressure) No catalyst Alkene is product
Different pollutant from burning fossil fuels, how it’s formed, problem it causes, ways to reduce the problem.
Equation for flue gas desulphur
The equation for catalytic converter
