Alkanes Flashcards
(27 cards)
What is the general formula for alkanes?
CnH2n+2
Are alkanes saturated or unsaturated?
They are saturated.
What is the shape of alkanes?
Tetrahedral
How many pairs of bonding electrons surround each carbon atom?
4
How do the bonding electrons repel each other?
They repel each other equally.
What is the bond angle of alkanes?
109.5
What are the properties of short alkanes?
Low boiling point
Gases at RTP
In what state are larger alkanes?
They are liquids.
What type of bonds are inside alkane molecules?
Covalent bonds.
What type of bonds are between the alkane molecules?
London forces
What do the London forces do to the molecules?
They hold them all together.
What increases the strength of the London forces?
The longer the carbon chain,the stronger the induced dipole-dipole interactions.
Why do the induced dipole-dipole interactions get stronger as the carbon chain gets longer?
There is more surface contact and more electrons to interact.
Why does the boiling point rise as the carbon chain gets longer?
It takes more energy to overcome the London forces.
Why do branched-chain alkanes have lower boiling points than their straight-chain isomers?
They can’t pack together as closely so there is a smaller molecular surface area, this reduces the strength of the London forces.
What happens if you oxidise alkanes?
You get carbon dioxide and water.
Do alkanes react completely in oxygen?
Yes
In what state do the combustion reactions of alkanes occur?
In gas.
What needs to happen to liquid alkanes before combustion?
They need to be vaporised.
What burns more easily, long chain alkanes or short chain alkanes?
Short chain alkanes as they are gases.
What is more volatile, long chain alkanes or short chain alkanes?
Short chain alkanes.
Why do larger alkanes release more energy per mole?
They have more bonds to react.
Why do alkanes make excellent fuels?
They release lots of energy when they burn.
What do all gases at the same temperature and pressure have in common?
Thy have the same molar volume when at the same temperature and pressure.
