Alkanes Flashcards
(24 cards)
What is a hydrocarbon ?
a compound that only contains hydrogen and carbon atoms
What is an unsaturated molecule ?
a hydrocarbon that contains one or more C=C bonds
What is a saturated molecule ?
a hydrocarbon that only contains C-C bonds
What is the general formula of an alkane ?
C n H (2n+2)
What is a homologous series ?
molecules with the same functional group, each successive member differing by CH2
What is functional group ?
the part of the molecule that is responsible for the chemical reactions
What is a structural isomer ?
molecules with the same molecular formula but a different structural formulae
Describe and explain the trend in boiling points of alkanes.
- boiling point increases as length of hydrocarbon chain increases
- the longer the chain, the more points of contact, so more London forces, which require more energy to overcome, and so boiling point increases
How are sigma bonds formed ?
direct overlap of s orbitals
Why are alkanes not very reactive ?
they have strong sigma bonds and are non-polar molecules
Why does incomplete combustion happen ?
there is an insufficient supply of oxygen
What is the problem with carbon monoxide ?
it is toxic as it prevents haemoglobin from binding to oxygen and so the body is starved of oxygen
What is complete combustion ?
when one mole of a substance reacts completely with oxygen
What is homolytic fission ?
when each of the bonded atoms takes one of the electrons from the shared pair of electrons in the covalent bond
What is a radical ?
an atom or group of atoms with an unpaired electron
What condition is needed for radical substitution ?
UV light
What happens in the initiation step ?
the reactant is split into two radicals
What happens in the propagation step ?
the radical reacts with the alkane to form an alkane radical, which reacts with the reactant to form the product and a radical of the reactant
What are the 3 termination steps ?
- the two reactant radicals react to form the reactant
- the reactant radical and alkane radical react
- two alkane radicals react
What are the limitations of free radical substitution ?
- substitution can happen at any point on the chain
- different termination steps can occur
- further substitution can occur
What causes CFCs to break down in the atmosphere ?
UV light from the sun
Why are CFCs stable ?
strong bonds
What causes nitrogen oxide to be formed in the atmosphere ?
- lightning
- aircraft
What is the overall equation for the breakdown of the ozone ?
O3 + O => O2
