16:Alkanes Flashcards
Definition of hydrocarbon
compounds that only contain carbon and hydrogen
What is a saturated organic compound
Contains only single bonds between carbon atoms
What is the prefix of a hydrocarbon with one carbon in the chain
meth-
What is the prefix of a hydrocarbon with two carbons in the chain
eth-
What is the prefix of a hydrocarbon with three carbons in the chain
prop-
What is the prefix of a hydrocarbon with four carbons in the chain
but-
What is the general formula for alkanes
Cn H₂n+₂
What is a functional group
An atom or group of atoms that gives a compound its characteristic chemical reactivity
What is a homologous series
A series of compounds that have the same functional group and the same general formula, and which successive members of the series differ by an extra CH₂ unit
eg. alkanes form a homologous series
What is a structural isomer
Compounds that have the same molecular formula but different structural formula
What is the general formula for cycloalkanes
Cn H₂n
What bonds are broken to melt or boil alkanes
Induced dipole-dipole bonds
Why do more carbons in an alkane increase the boiling point
The surface area of contact increases so there are more induced dipole-dipole formed
Why do straight chain alkanes have higher boiling points than isomers with more branches
The surface area of contact is higher so there are more induced dipole-dipole formed
Are alkanes more or less dense than water
Less
they will float on water
Why are alkanes virtually insoluble in water
They are non-polar so cannot form hydrogen bonds
What is the equation for complete combustion of alkanes
Complete combustion of propene
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
What is the equation for incomplete combustion of alkanes
Incomplete combustion of propene
C₃H₈ + 3 1/2O₂ → 3CO + 4H₂O
or
C₃H₈ + 2O₂ → 3C + 4H₂O
What are the products of the complete combustion of alkanes
CO₂ + H₂O
What are the products of the incomplete complete combustion of alkanes
CO + H₂O
or
C + H₂O
Why is carbon monoxide toxic
It binds to haemoglobin in blood thus limiting the supply of oxygen
What are the key condition for substitution reactions
They need exposure to UV light
What is a radical
An atom or group of atoms which has an unpaired electron
What are the 3 stages of the mechanism of radical substitution
Initiation
Propagation
Termination
What is homolytic fission
A process in which a covalent bond breaks so that one of the electrons that made up the bond stays with one of the atoms and the other electron stays with the other atom
What happens in the initiation stage of radical substitution
The fission of a halogen molecule
eg. Cl₂(g) → Cl•(g) + Cl•(g)
What happens in the propagation stage of radical substitution
1) The halogen radical reacts with the alkane
eg. Cl•(g) + CH₄(g) → HCl(g) + •CH₃(g)
2) The alkane radical reacts with the halogen molecule
eg. •CH₃(g) + Cl₂(g) → CH₃Cl(g) + Cl•(g)
What happens in the termination stage of radical substitution
Two radicals collide and combine to form a molecule
eg. 1) Cl• + Cl• → Cl₂
2) •CH₃ + •CH₃ → C₂H₆
3) Cl• + •CH₃ → CH₃Cl
