Final answer:
The compound used alongside aluminium to join railway tracks is iron(III) oxide (Fe2O3), involved in the thermite reaction which is exothermic and produces molten iron for welding tracks together.
Step-by-step explanation:
The compound used with aluminium to join railway tracks is Fe2O3, which is iron(III) oxide. The reaction of aluminium with Fe2O3 is known as the thermite reaction, an exothermic chemical reaction that produces molten iron through the reduction of iron oxide by aluminium:
Al(s) + Fe2O3(s) → Al2O3(s) + Fe(l)
This reaction releases a lot of heat, enough to melt the iron which can then be used to join the railway tracks. It's a process that demonstrates a real-world application of an exothermic redox reaction which can be represented through physical modeling using balls and sticks, jelly tots and toothpicks, or simple drawings to visualize the reactants and products involved.