why does the presence of pi bonds make alkenes more reactive
the pi bond of the c=c bond requires less energy to break c-c single bond and so reacts more readily
c-c single bond enthalpy value
347^kJ mol-1
equates to sigma bond portion of c=c bond
c=c double bond enthalpy value
612 kJ mol-1
value of sigma and pi
pi bond enthalpy
612 - 347 = 265 kJ mol-1
what does the calc for pi bond show
that the pi bond of c=c bond is weaker than c-c bond explains why alkenes are more reactive
why are alenes used as starting molecules when making new compounds
they can undergo many types of reactions
what is hydrogenation/reduction
the reaction between alkene and hydrogen
what does hydrogenation require
nickel catalyst, temp - 200C, pressure - 1000kPa
what does catalytic hydrogenation do
convert alkenes into useful alkanes
what does hydrogenation importantly applied to
the production of margarine from vegetable oils
why are vegetable oils suited to make margarine
vege oil are unsaturated and may be hydrogenated to make margarine which has a higher melting point due to stronger london forces
how can vege oil turn to margarine
by controlling the conditions it is possible to restrict how many c=c bonds are broken and produce partially hydrogenated vege oil whcihc have the desired properties and texture for maragarine manufacture
what is halogenation
the reation between the alkenes and the halogens known as the halogenation
its is an example of electrophillic addition where an electrophile joins into a double bond
what happens in halogenation
when the c=c double bond is broken and a new single bond is formed from each of the two carbon atoms
reults in dihaloalkane
reacts readily at room temperature and basis for the test for saturation in molecules
what can halogens be used to test for
they can be used to test id=f a molecule is unsaturated(contains a double bons)
