Before considering the reactions of alkenes, it is vital to get familiar with the properties of them. In terms of organic chemistry, alkenes are unsaturated chemical compounds, which contain at least one carbon-carbon double bond. The simpler acyclic alkenes that contain only one double bond without any other functional group usually form a homologous chain of hydrocarbons with the formula CnH2n.  The simplest form of the alkenes is ethylene, which has the IUPAC name ethene. However, sometimes aromatic compounds are also termed as cyclic alkenes, but they are not the alkenes as the reactions of alkenes are quite different from them.   

Well, that was all about the introduction to alkenes. Now, let’s consider their physical properties which are essential to keep in mind before approaching the reactions of alkenes. The physical state of alkenes depends upon the number of carbons presented in them. For instance, the simplest alkenes including propene, butene and ethene, which hold the number of carbon below five, are gas. Whereas the linear alkenes which possess around five to sixteen carbons are in the form of liquids and the higher alkenes are found in the solid state. Now, when it comes to the reactions of alkenes, they are quite reactive than the alkanes.
The reason behind this reactivity is the presence of a carbon-carbon pi bond in these alkenes. Almost, all the reactions of alkenes involve shattering of this particular pi bond, which leads the formation of a new single compound. Basically, all the reactions of alkenes could be classified under the three categories which are addition reactions, oxidation reactions and polymerization.

Now, let’s talk about the addition reactions of alkenes, which occur due to the opening of double bond of carbon. These addition reactions could be divided into the subcategories of catalytic addition of hydrogen, electrophilic addition, halogenation and hydrohalogenation. In the catalytic hydrogenation reactions of alkenes, the corresponding alkane is produced in the presence of some metallic catalyst. For example, the reaction of ethene with the hydrogen under the pressure produces the molecule of ethane.
    CH2=CH2 + H2 → CH3-CH3

The next important mechanism for the reactions of alkenes is the electrophilic addition, which is followed by the majority of the addition reactions. Apart from this, hydrohalogenation of the alkenes also lies in the category of addition reactions, which forms the halo-alkanes. The next type of the reactions of alkenes is oxidization in which alkenes react with several oxidizing agents. These different oxidizing agents such as oxygen etc. lead the formation of different products, which are distinct from each other. For instance, alkenes burn with a brighter flame in the existence of oxygen, which forms two products carbon-dioxide and water. And in case of reaction with percarboxylic acids, alkenes provide epoxides as the products.