Children's conception of changes in the state of matter: From liquid (or solid) to gas

This research examines children's (ages 9–15) conception of changes in the state of matter from liquid or solid to gas, as well as their understanding of the reversibility of this process. Children were tested for their ability to conserve matter, its identity, and its weight in tasks using evaporation of acetone and sublimation of iodine. It was found that children who recognized weight conservation in one of the tasks did not necessarily recognize the same in the second task. Students believed that gas has no weight, or that gas is lighter than the same material in its liquid or solid state. In addition, students who recognized weight conservation were not always aware of the reversibility of the process. Until the age of 12 specific perceptual input from the task (e.g., color) dramatically influenced students' responses to the conservation of weight task. The relationship between children's intuitive ideas about matter, as observed in this study, and their logical ability to conserve weight, as observed in this study, is discussed.