Introduction:
When an alkene is passed through a red-hot iron tube, it undergoes a process known as thermal cracking. This process involves the breaking of large hydrocarbon molecules into smaller, more useful hydrocarbon molecules.

Key Points:
- Alkenes are unsaturated hydrocarbons with a carbon-carbon double bond.
- Passing alkene through a red-hot iron tube causes the double bond to break, leading to the formation of smaller hydrocarbons.

Process of Thermal Cracking:
- The alkene molecule is heated as it passes through the red-hot iron tube.
- The high temperature causes the carbon-carbon double bond in the alkene to break.
- This results in the formation of smaller hydrocarbon molecules such as alkanes, alkenes, and hydrogen gas.
- The process is known as thermal cracking because it involves the breaking of larger hydrocarbon molecules into smaller ones through the application of heat.

Importance of Thermal Cracking:
- Thermal cracking is an important process in the petrochemical industry as it allows for the production of valuable products such as gasoline, diesel, and other fuels.
- By breaking down larger hydrocarbons into smaller ones, thermal cracking helps in maximizing the yield of useful products from crude oil.
Overall, passing an alkene through a red-hot iron tube results in thermal cracking, a process that breaks down the alkene into smaller hydrocarbon molecules through the application of heat. This process is crucial for the production of various fuels and petrochemical products.