Chemical reactions are described as those that form new products. An example of burning sparklers is given. The word equation forming magnesium oxide is mentioned and the concept of conservation of mass in chemical reactions is introduced. This is consolidated by using the thermal decomposition of calcium carbonate.

First broadcast:
25 March 2003

Introduce the concept of conservation of mass in chemical reactions. Students could be encouraged to copy the word equations throughout the clip and try and write them as chemical equations. As a practical exercise, a series of reactions could be carried out in class, with the reactants and products weighed. Where a perceived change has occurred, discuss why this might be the case, for example through the creation of gases. Repeat reactions that create gas in contained conditions to show the mass does not change. The conservation of mass could be discussed in relation to the combustion of hydrocarbons.