Alkanes Flashcards
what are alkanes?
a homologous series of saturated hydrocarbons
general formula of alkanes?
CnH2n+2
reactivity of alkanes?
very unreactive, although do burn and react with halogens
how does length of alkane affect boiling point? why?
longer carbon chain = higher b.p.
because stronger van der Waals’ forces
isomers of alkanes can have branched chains- how does this affect the boiling point? why?
more branched chains = lower b.p.
because have weaker van der Waals’ forces (molecules can’t pack as close)
what is the angle on unbranched C-C-C chains?
109.5 degrees
what is the general formula for ring alkanes?
CnH2n
are alkanes polar?
almost non-polar as the electronegativities of carbon and hydrogen are so similar
what intermolecular forces exist between alkane molecules?
only van der waals
how do the strength of intermolecular forces change with the size of alkanes?
larger alkane molecule = stronger van der waals forces
how does the boiling point of alkanes change with temperature and why?
increased chain length = increased boiling point, because stronger van ser waals forces
what state are shorter chain alkanes at room temperature?
gases
at what chain length do alkanes becomes solids at room temperature?
18
how does branching affect the melting point of an alkane? why?
alkanes with branched chains have lower melting points than straight chain alkanes (with same no. of carbons). this is because branched chain alkanes cannot pack together so closely, so the vdw forces are not as effective
are alkanes soluble in water? why?
insoluble. because water molecules are held together by hydrogen bonds, much stronger than the vdw forces between alkane molecules.
