The Zimbabwe Secondary School Science Project (ZIM-SCI) developed student study guides, corresponding teaching guides, and science kits for a low-cost science course which could be taught during the first 2 years of secondary school without the aid of qualified teachers and conventional laboratories. This ZIM-SCI study guide is a four-part unit consisting of activities and experiments in which students investigate: (1) the three states of matter (solids, liquids, and gases) and kinetic theory; (2) expansion and diffusion; (3) the behavior of gases; and (4) chemical reactions. Information to help students understand the scientific principles behind the activities and experiments is included throughout the unit. (JN)