Complete the hydrogenation reaction. $$ \mathrm{CH}_{2}=\mathrm{CH}_{2}+\mathrm{H}_{2} \longrightarrow $$

Organic chemistry is a sub-discipline within chemistry that involves the study of the structure, properties, composition, reactions, and synthesis of organic compounds, which are defined by the presence of carbon atoms. In organic molecules, carbon atoms can form a variety of bonds, including single, double, and triple bonds, allowing for the creation of a vast range of compounds with differing properties.

Due to the versatility of carbon atoms, organic chemistry is integral to many industries such as pharmaceuticals, petrochemicals, and materials science. Understanding the fundamentals of how organic compounds react through chemical reactions is pivotal in the creation and modification of molecules that serve various purposes in day-to-day life as well as in advanced technological applications.

Alkenes are a group of hydrocarbons that contain at least one carbon-carbon double bond, which is signified by the suffix '-ene' in their names. These unsaturated compounds are characterized by a higher reactivity compared to alkanes, which are saturated hydrocarbons with only single bonds.

In alkenes, the presence of the double bond creates a region of electron density that can be targeted by electrophiles in chemical reactions. This feature makes alkenes more reactive and allows for various transformations, such as polymerization, oxidation, and halogenation. However, one of the most fundamental reactions involving alkenes is hydrogenation, where the double bond is saturated by the addition of hydrogen.

Chemical reactions are processes where reactants are transformed into products through the breaking and forming of chemical bonds. These changes can result in the transfer of energy and the production of new substances with different physical and chemical properties than the reactants.

Reactions are influenced by factors such as temperature, pressure, concentration, and the presence of catalysts. Hydrogenation is a type of addition reaction where hydrogen molecules are added to double or triple bonds in unsaturated compounds, typically in the presence of metal catalysts like nickel, palladium, or platinum, to produce a saturated molecule. The catalyst operates by facilitating the adsorption of the hydrogen molecules, helping to break the double bond and allow for the connection with hydrogen atoms.