Explain why the chemical process that takes place in an icepack containing ammonium chloride is not a chemical reaction.

When you "Pop" and ice pack, you are allowing the water to dissolve the ammonium chloride. The act of dissolving the ammonium chloride is endothermic, which causes the solution to get cold. No chemical change has occured to the ammonium chloride. If you were to take the contained solution and evaporate the water, you would be left with ammonium chloride, which is what you started with.