Matter and Chemical Reactions — Chemical Reactions

About this lesson

This unit introduces the concept of chemical reactions, distinguishing them from physical changes. It defines a chemical reaction as the process of breaking bonds between atoms of reactants and forming new bonds to create products with different properties. The text provides several practical activities to demonstrate evidence of chemical reactions, including the formation of a precipitate (silver chloride), a colour change (zinc in copper sulphate solution), evolution of gas (magnesium with hydrochloric acid), and emission of light and heat (burning magnesium). It also explores how the properties of substances change before and after a reaction, using examples like burning sugar and reacting oil with caustic soda to form soap. Real-life examples are given, such as cooking meat, frying eggs, cut apples turning brown, rusting iron, and fireworks. The unit includes laboratory safety precautions and critical thinking questions about whether certain changes (like a water bottle breaking in a freezer) are chemical reactions. By the end, a student should be able to understand the concept and mechanism of chemical reactions, identify evidence of their occurrence, compare properties before and after, and give real-life examples. The text also includes evaluation questions and a research activity on everyday chemical reactions.