Cracking & Alkenes Flashcards

All 9 cards in this deck

What is cracking?

Breaking down large hydrocarbon molecules into smaller, more useful molecules.

What are the conditions used for catalytic cracking?

Heat the hydrocarbon to vaporise it and pass the vapour over a hot catalyst.

What are the conditions used for steam cracking?

Vaporise the hydrocarbon, mix it with steam and heat to a very high temperature.

Which two types of hydrocarbon are produced by cracking?

Alkanes and alkenes.

Why is cracking carried out in industry?

Demand for small hydrocarbons (fuels) is greater than the supply, and cracking also makes alkenes for polymers and other chemicals.

What is the test for an alkene, and the colour change seen?

Add bromine water: it changes from orange to colourless.

True or false? Alkanes decolourise bromine water.

False. Alkenes are more reactive and decolourise bromine water; alkanes leave it orange.

How do you balance an equation for a cracking reaction?

e.g. $\mathrm{C_{10}H_{22} \rightarrow C_8H_{18} + \;?}$

1. Count carbons on each side: $10 - 8 = 2$ left over.
2. Count hydrogens: $22 - 18 = 4$ left over.
3. Missing product is $\mathrm{C_2H_4}$: $\mathrm{C_{10}H_{22} \rightarrow C_8H_{18} + C_2H_4}$

True or false? Alkenes are more reactive than alkanes.

True. Their greater reactivity is why alkenes react with bromine water but alkanes do not.