1) The shorter hydrocarbons are more useful as they are easier to ignite and less viscous (they flow more easily)
2) Shorter, longer, longer, shorter, longer, shorter
There is a greater demand for SHORTER hydrocarbons compared to LONGER hydrocarbons. Supply is greater than demand for LONGER hydrocarbons. Demand is greater than supply for SHORTER hydrocarbons. Cracking breaks down LONGER hydrocarbons into SHORTER hydrocarbons.
b) Thermal decomposition reaction (this means that a substance breaks down with heat)
4) Heat up the longer chained hydrocarbon that you want to crack so that it turns into a gas (vaporise them)
Pass the vaporised hydrocarbon over a powdered catalyst (sometimes aluminium oxide)
Thermal decomposition occurs and the longer chained hydrocarbon splits up into smaller hydrocarbons
C12H26 –> C10H22 + C2H4
b) Create polymers
c) C12H26 –> C9H20 + C3H6
C10H22 –> C7H16 + C3H6
C12H26 –> C8H18 + 2 C2H4
C16H34 –> C10H22 + 3 C2H4
10) C17H36 –> C8H18 + 3 C3H6
1) Out of shorter and longer hydrocarbons, which are more useful? Explain your answer.
2) Fill in the gaps below with the words “shorter” and “longer”. You will use each word 3 times.
There is a greater demand for _______ hydrocarbons compared to _______ hydrocarbons. Supply is greater than demand for _______ hydrocarbons. Demand is greater than supply for _______ hydrocarbons. Cracking breaks down _______ hydrocarbons into _______ hydrocarbons.
a) Is cracking an exothermic or endothermic reaction?
b) What type of reaction is cracking?
4) Describe the steps in catalytic cracking.
5) The cracking of dodecane (C12H26) produces ethene (C2H4) and one other hydrocarbon. The partially completed chemical equation is shown below.
C12H26 –> _______ + C2H4
a) Find the molecular formula for the other hydrocarbon.
b) Give one use for the ethene that is produced by cracking dodecane.
c) A different molecule of dodecane is cracked. This time it produces propene (C3H6) and one other hydrocarbon. Write the balanced chemical equation for this taking place.
6) The cracking of decane (C10H22) produces heptane (C7H16) and one other hydrocarbon. The partially completed chemical equation is shown below.
C10H22 –> C7H16 + ______
Complete the chemical equation.
7) Is the statement below true or false?
“cracking is used to match supply with demand”
8) The hydrocarbon C12H26 can be cracked. Balance the cracking equation below.
C12H26 –> C8H18 + __ C2H4
9) The hydrocarbon C16H34 can be cracked. Balance the cracking equation below.
C16H34 –> C10H22 + __ C2H4
10) The hydrocarbon C17H36 can be cracked to produce a single octane molecule (C8H18) and many propene molecules (C3H6). Write the balanced cracking equation for this.