With the help of an example, explain the process of hydrogenation. Mention the essential conditions for the reaction and state the change in physical property with the formation of the product.

Hydrogenation is an addition reaction where unsaturated hydrocarbons (alkenes or alkynes) add hydrogen in the presence of catalysts to become saturated hydrocarbons.

Example: The addition of hydrogen to ethene to form ethane.

$$CH_2=CH_2 + H_2 \xrightarrow{Ni/Pd} CH_3-CH_3$$

Essential Conditions:

1. Presence of a catalyst such as Nickel ($Ni$), Palladium ($Pd$), or Platinum ($Pt$).
2. Presence of unsaturated carbon-carbon bonds (double or triple bonds).

Change in Physical Property:

This process is used to convert liquid vegetable oils (which are unsaturated) into solid vegetable ghee (which is saturated). Thus, the physical state changes from liquid to solid/semi-solid.