1. How does the mass change within a chemical reaction?

2. Learning Objectives
Aiming for 4: Understand that in a reaction the number of atoms of each element remains unchanged.
Aiming for 6: Explain any observed changes in mass in a non-enclosed system during a chemical reaction.
Aiming for 8: Explain any observed changes in mass relating to the particle model.

3. Open and Closed Systems
Open systems – can freely exchange energy and matter with their surroundings e.g. a saucepan cooking on the stove.
Closed systems – can only exchange energy with their surrounding and not matter e.g. putting a lid on a saucepan cooking on the stove.
Isolated systems – do not allow the exchange of energy or matter within the system to its surrounds e.g. a thermos flask.