Give examples of reactions that appear to involve a change in mass.
When a metal reacts with oxygen, the mass of the metal oxide produced is greater than the mass of the metal you started with.
When metal carbonates thermally decompose, carbon dioxide is produced and escapes into the atmosphere leaving the metal oxide as the only solid product.
Some reactions may appear to involve a change in mass but this can usually be explained because a reactant or product is a gas and its mass has not been taken into account.
