11.5 Alkenes
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41. Describe the bonding in alkenes and their classification as hydrocarbons.
They include at least one reactive double carbonācarbon covalent bond (C=C) and are classified as unsaturated hydrocarbons.
42. How are alkenes and hydrogen manufactured?
By thermal or catalytic cracking of long-chain alkane fractions at high operational temperatures using a catalyst (such as Al2O3).
43. Why are larger alkane molecules cracked?
To produce shorter, more high-demand molecules like alkenes (crucial for polymer addition chains) and hydrogen gas.
44. How can you distinguish between saturated and unsaturated hydrocarbons using a chemical test?
By treating with aqueous bromine (Br2(aq)); unsaturated compounds will rapidly decolourise the bromine solution from orange-brown to colorless.
45. Define an addition reaction.
A chemical reaction in which multiple combining reactant molecules yield exactly one single product.
46. Name the three substances that alkenes react with in addition reactions as stated in the syllabus.
Bromine (Br2), hydrogen (H2), and steam (H2O).