Cracking and Making Useful Hydrocarbons Flashcards

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What is meant by cracking a hydrocarbon?

Cracking is breaking up large hydrocarbon molecules into smaller, more useful ones by heating them, usually with a catalyst.

Why do oil companies crack long-chain hydrocarbons?

They crack long-chain hydrocarbons to make more of the short-chain fuels and alkenes that are in higher demand and are more useful.

What type of reaction is cracking?

Cracking is a thermal decomposition reaction, where one substance breaks down into simpler substances when it is heated.

What are the main conditions needed for catalytic cracking?

The hydrocarbons are heated until they are a gas and then passed over a hot catalyst, such as silica or alumina, at a high temperature.

What two types of hydrocarbons are made when an alkane is cracked?

Cracking makes a mixture of smaller alkanes and alkenes.

Why are short-chain alkanes useful products from cracking?

Short-chain alkanes are very flammable and burn cleanly, so they are useful as fuels such as petrol and propane.

Why are alkenes made in cracking useful?

Alkenes are more reactive than alkanes, so they are useful as starting materials to make polymers (plastics) and other chemicals.

In a cracking reaction, what must stay the same before and after the reaction?

The total number of each type of atom, such as carbon and hydrogen, must stay the same because atoms are not created or destroyed.

Complete this cracking equation: C10H22 → C8H18 + ?

The missing product is C2H4 (ethene), an alkene, so that the total numbers of carbon and hydrogen atoms match.

Describe simply how catalytic cracking is carried out in an oil refinery.

A heavy oil fraction is heated until it turns into a gas, then the hot gas is passed over a solid catalyst so the large molecules split into smaller ones.