Question

When alkanes and alkenes react, they react by substitution or addition. What is meant by the substitution and addition reactions?

Answer 1

Consider the following explanation.

Explanation:

Alkanes are the hydrocarbons having carbon carbon double bonds only. Due to being saturated, they give Substitution Reactions.

Substitution reactions are the ones in which the Hydrogen atom of an alkane is substituted/replaced by another atom or group of atoms(functional groups).

For example: When ethane reacts with halogen(chlorine in this example) in the presence of diffused sunlight, ethylchloride is formed along with the liberation of hydrogenchloride.

`CH_3CH_3` `+` `Cl_2` `->` `CH_3CH_2Cl` `+` `HCl`

Alkenes are the hydrocarbons having atleast one carbon carbon double bond. Since they are unsaturated, they have the tendency to undergo Addition instead of Substitution reactions.

Addition reactions are the ones in which atoms or group of atoms are added to the molecule with the breakage of double bonds in alkenes and tripple bonds in alkynes to form a larger molecule.

For example: when ethene reacts with chlorine, following addition reaction occurs.

Hope this explanation takes you somewhere! :)