4.1.2 Alkanes Flashcards
What happens during orbital hybridisation?
When the orbitals mix together to form new hybrid orbitals.
Explain the correlation between boiling point and chain length in alkanes.
As the chain length increases so does the surface area of contact between molecules, this means there is more London dispersion forces so more energy is needed to overcome the forces.
How does branching affect bp?
Less surface area of contact between molecules.
What are alkanes?
The alkanes are saturated hydrocarbons containing single C-C and C-H bonds as sigma bonds
What are cycloalkanes?
The cycloalkanes are a homologous series of hydrocarbons with the general formula CnH2n and names beginning cyclo– and ending in –ane.
What is bond enthalpy?
the amount of energy required to break one mole of a specific covalent bond in a gaseous molecule
Why are alkanes general unreactive? Give 2 reasons.
1) C-C and C-H bonds have high bond enthalpy which means there relatively difficult to break.
2) C-C bonds are non polar so C-H bonds have high polarity.
In what order do you balance in combustion?
Carbon
Hydrogen
oxygen
What would happen if there was even less oxygen then needed incomplete combustion?
Carbon particulates are formed.
Why is carbon monoxide dangerous for the body?
It binds with the haemoglobin and is carried instead of oxygen.
what is a fuel?
a substance when burned releases heat energy
3 types of cracking
thermal
steam
catalyst
Why do cycloalkanes have higher bp then its straight chain alkane?
There is a strain in the molecule which means more energy to break London dispersion forces.
What type of isomer is a cycloalkene
structural isomer
Features/quality of alkanes:
non polar
insoluble in water
less dense then water
hydrophobic it repels in water
cannot conduct - all e- used
no e- can move
low mp
simple covalent
What are the 3 main types of attackers and what do they do?
nucleophile - donates a lone pair of electron to an electron deficient area (to form a new bond)
Electrophile - electron pair acceptor
radical - unpaired electrons usual reactive
What is it called when chemical reaction bonds are broken?
bond fission
2 types of bond fission?
Hetrolytic and homolytic
Conditions for free radical substitution?
Uv light
Excess methane to reduce further substitution?
What is a mechanism
Multiple steps to a reaction
What happens in the initiation step?
The starting of the reaction that produces 2 radicals using uv - homiletic fission
What happens in propagation?
A 2 step process that combine to form an overall equation where the same species cancel out. Has to be 2 radicals on each side of the equation
Termination step?
The 2 radicals react together
Why is the initiation step an example of homolytic fission?
Because one election from bond pair goes to each atom/ forms two radicals
Difference in terms of intermolecular forces of alkanes compared to alcohols.
Alcohol have hydrogen bonding and London dispersion forces but the hydrogen bonding is stronger then the alkanes ldf.
what is meant by homologous series?
A series of compound elements with the same functional group with successive members differering by ch2
explain why the mechanism for free radical substitution is likely to produce a mixture of organic products?
it can substitute any of h atoms
