What would the student see when the reaction takes place?

Your question is not specific enough so, I've given you a list of things that occurs, when a reaction has taken place.

It could be in the form of:

Heat or light given off or a colour change.

Hope this helps!

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.