What are some clues to some events to show that a chemical change is occuring?

Question

Describe some clues you might observe during the following events that could support the conclusion that a chemical change is occuring:
a. An antacid tablet is dropped into water
b. A ring of scum forms around a bathtub
c. Iron rusts
d. a firecracker explodes

I am stuck on this question on my homework and would appreciate if someone helps me. Thanks!!!

Answer 1

a. Fizzing. The bubbling of gas to the top of the water from the antacid tablet.
b. Soap isn't complete dissolvable in the water. That mixed with body oil (also undissovable) begins to build up and form a layer around the tub.
c. Fe + H2O --> Fe2O3 (rust) - when iron turns to rust it is a chemical reaction with the water or water vapor in the air.
d. Combustion reaction. Spark + O2 + (whatever gun powder) ---> CO2 + H2O + etc(in some cases)

Answer 2

a. A gas evolves (CO2)

b. A precipitate forms (Ca or Mg soap)

c. A different compound (red oxide) appears

d. An oxidation-reduction reaction occurs (KNO3oxidizes C and S)