Chemical reactions are useful in cooking and help to improve the taste of food. Cooking and chemistry have quite a bit in common. The starting materials in a chemical reaction are called the reactants. These react with each other to form a completely new substance known as the product. Products have very different properties to the reactants. Cakes are firmer and taste better than the individual reactants. The colour is different too. Not all chemical reactions need heat energy to make them happen. When bicarbonate of soda and vinegar are mixed, the chemical reaction produces a gas.

First broadcast:
11 October 2007

Pupils could replicate the activities they see modelled in the clip, experimenting with bicarbonate of soda and vinegar, as well as following a recipe to mix and bake cakes or biscuits. Ask: "Were these chemical changes reversible or irreversible?" (They were irreversible - you can't return the cake to its original ingredients, or put the gas released back into the sodium bicarbonate powder.) Encourage pupils to use the correct scientific vocabulary to describe the changes they see. They should use the terms: reaction, reactant, substance, product, solid, liquid and gas.