Law on conservation of mass

Question 1

Evidence of chemical reactions

Answer 1

Any one of the following clues MAY indicate that a chemical change has produced one or more new substances:
Change in colour
Energy is released or absorbed
A gas is produced
A precipitate forms
The only way to be certain that a chemical change has occurred is to test the product to show that it is a new substance!

Question 2

Law of conservation of Mass

Answer 2

Law of Conservation of Mass: during a chemical reaction, the total mass of reactants equals the total mass of products
In other words, every atom present in the reactants must also be present in the products!