Why is diene more reactive than alkene? The chemical reduction of 1,3-butadiene with sodium in alcohol gives mainly the 1,4-addition product that is but-2-ene.
Under these condition the isolated double bond are not reduced. This suggest that dienes are much more reactive than simple alkenes.

Why is diene more reactive than alkene even though the conjugated double bond of diene (in the example of excerpts given above) is stabilized with resonance?
How is 1,4-addition product the major product?
It is not only the diene itself which is stabilised by resonance, but on electrophilic addition the carbocation formed is also stabilised by resonance if the diene is conjugated. Thus, forming the intermediate for a conjugated diene is easier than forming the intermediate for the alkene, even though the starting compound itself is more stable in case of conjugated dienes and therefore conjugated dienes react faster.