alkanes Flashcards
define alkane
saturated hydrocarbon
draw how a sigma bond is formed in alkanes
what happens to boiling point as alkanes get longer?
increase
why does boiling point increase as alkanes get longer?
ncreasing
number of electrons in the bigger molecules causing an increase in the size of the induced dipole–dipole
interactions (London forces) between molecules.
how does shape of molecuke effect the size of the london forces?
Long chain alkanes have a larger surface area of contact between molecules for London forces to form than compared to spherical shaped branched alkanes and so have stronger induced dipole–dipole interactions and higher boiling points.
The low reactivity of alkanes with many reagents can be explained by the ____ bond enthalpies of the C-C
and C-H bonds and the ____ of the σ-bonds present.
high, very low polarity
describe complete combustion of alkanes
The products of complete combustion are CO2 and H2O.
- highly exothermic = fuels
describe incomplete combustion of alkanes
producing CO (which is very toxic) and/or C (producing a sooty flame)
why is CO toxic?
CO is toxic to humans as CO can from a strong bond with haemoglobin in red blood cells. This is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin.
define cracking
conversion of large hydrocarbons to smaller molecules by breaking C-C bonds
what is the mechanism for reaction of alkanes with bromine/ chlorine in UV light
free radical substitution
describe initiation
UV light, the bond has broken in a process called homolytic fission, forms free radicals
write mechanism of Br2 and Propane
Write the overall reaction equation for the formation of CCl4 from CH4 + Cl2
CH4 + 4 Cl2 –> CCl4 + 4 HCl
Write the overall reaction equation for the formation of CFCl3 from CH3F + Cl2
CH3F + 3 Cl2 –> CFCl3 + 3 HCl
draw 3-ethyl-2,4-dimethylhexane
