What is cracking in chemistry?
The breaking of large hydrocarbon molecules into smaller, more useful molecules.
AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Higher · 5.7.1.4
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What is cracking in chemistry?
The breaking of large hydrocarbon molecules into smaller, more useful molecules.
Why are long-chain hydrocarbons from crude oil cracked?
They are often less useful or less in demand than smaller molecules.
What happens to carbon–carbon bonds when hydrocarbon vapour is heated during cracking?
Some carbon–carbon bonds break.
How is catalytic cracking carried out?
Hydrocarbon vapour is passed over a hot catalyst at a high temperature.
How is steam cracking carried out?
Hydrocarbon vapour is mixed with steam and heated to a very high temperature.
What types of hydrocarbons are found in the products of cracking?
A mixture of smaller hydrocarbons, including alkanes and alkenes.
What must be equal on both sides of a balanced cracking equation?
The total number of atoms of each element.
Why is cracking useful?
It converts less useful large hydrocarbons into products in greater demand.
What are small hydrocarbon molecules produced by cracking used for?
As fuels, including for transport and heating.
What are alkenes produced by cracking used to make?
Polymers, including plastics.
Besides making polymers, what role do alkenes play in chemical manufacturing?
They are starting materials for many other chemicals.
What is an alkene?
A hydrocarbon containing a carbon–carbon double bond.
Why are alkenes more reactive than alkanes?
Their carbon–carbon double bond reacts more easily than the single bonds in alkanes.
What type of reactive hydrocarbon can be produced by cracking?
Alkenes.
What happens when bromine water is added to an alkene?
It reacts and changes from orange to colourless.
What makes a chemical equation balanced?
Each element has the same number of atoms on both sides, reflecting conservation of atoms.
What does a coefficient before a chemical formula indicate?
The relative number of particles of that substance.
How does a coefficient affect the atom counts in the formula that follows it?
It multiplies every atom count in the formula.
What steps are used to balance a chemical equation?
Count each element’s atoms on both sides, adjust coefficients, then recount to check. Use the simplest whole-number coefficients.
Why must subscripts in chemical formulae not be changed when balancing an equation?
Changing them would change the substances represented.