DF5: Getting the right sized molecules

What is cracking

process of breaking large hydrocarbon molecules into smaller ones

What is the purpose of cracking

To match the supply of long-chain hydrocarbons with the demand for shorter-chain hydrocarbons like petrol

What are the two main types of cracking

Thermal cracking and catalytic cracking

What are the conditions for thermal cracking

High temperature

high pressure

What is a free radical

A molecule or atom with an unpaired electron

What are the products of thermal cracking

Alkenes and sometimes smaller alkanes

What are the conditions for catalytic cracking

Lower temperatures (720 K) and pressures with a zeolite catalyst

What are the products of catalytic cracking

Branched alkanes

What is a catalyst

A substance that speeds up a chemical reaction by providing an alternative pathway with a lower activation energy

What are zeolites

Zeolites are minerals with a porous structure

Describe the stages of heterogeneous catalysis

1. Reactants get adsorbed onto the catalyst surface. Bonds are weakened.

2. Bonds in the reactants break.

3. New bonds form to create the products.

4. The second bond forms, and the product diffuses away from the catalyst surface, leaving it free to adsorb fresh reactants.

What is catalyst poisoning

when impurities bind to the surface of a catalyst and stop it functioning

What is an example of a catalytic process in industry

The cracking of hydrocarbons using zeolite catalysts

Why are zeolites used as catalysts

Zeolites have a large surface area and a porous structure that allows selective cracking of molecules

Write the chemical equation for cracking of decane to form octane and ethene

C10H22 → C8H18 + C2H4

What is the role of a catalyst in the chemical industry

Catalysts help lower energy costs by allowing reactions to occur at lower temperatures and pressures