This mini-lesson covers Reactivity 3.3 & 3.4 at SL: radical substitution, combustion, electrophilic addition to alkenes, nucleophilic substitution of halogenoalkanes, and addition polymerisation.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
Alkanes are unreactive but react with halogens in UV light by radical substitution. UV causes homolytic fission (each atom keeps one electron), forming reactive radicals. The mechanism has three stages: initiation, propagation and termination.
Alkanes are good fuels. Complete combustion (plenty of oxygen) gives CO₂ and H₂O; incomplete combustion gives CO (toxic) or soot. Balance the equation to find the oxygen needed.
Alkenes are unsaturated: the electron-rich C=C reacts with electrophiles by addition — the double bond opens and atoms add across it. Adding bromine decolourises orange bromine water: the classic test for a C=C bond. Alkenes also add H₂ (hydrogenation), HX and H₂O.
Halogenoalkanes have a polar C–X bond (δ+ carbon). A nucleophile (electron-pair donor, e.g. OH⁻) attacks the δ+ carbon and substitutes for the halogen, forming an alcohol. This is nucleophilic substitution.
Many alkene monomers join by addition polymerisation: the C=C bonds open and link into a long saturated chain (e.g. ethene → poly(ethene)). No small molecule is lost.
Tap a reaction, then its type.
Tap an item on the left, then its match on the right.
Radicals (3.3): alkane + halogen under UV; homolytic fission; initiation/propagation/termination
Combustion: complete → CO₂ + H₂O; incomplete → CO/soot
Addition (3.4): alkene C=C + electrophile; bromine-water test for unsaturation
Substitution (3.4): halogenoalkane + nucleophile (OH⁻) → alcohol; alkenes → addition polymers
You've covered Mechanisms of chemical change for IB Diploma Chemistry SL. Press Finish to see your score.
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Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.