Normally there is evidence if a chemical reaction has taken places because sometimes you might see:
- A change in colour
- A precipate
- A gas given off
- A rise or fall in temperature
Rusting is a chemical reaction where a material containg iron (ferrous) rusts.
Combustion is another word for burning.
Acid reactions can be useful e.g the manufacturing industry or useless e.g corrosion
In a chemical reaction mass is conserved because the total number of atoms stay the same.