Praxis Elementary Education: Science (5005) Practice Test

The melting of ice is a clear example of a physical change because it involves a change in the state of matter without altering the chemical composition of the substance. When ice melts, it transforms from a solid to a liquid; however, the molecules remain as water (H2O) both before and after the change. Physical changes typically include phase changes like melting, freezing, evaporation, and condensation, where the substance retains its original chemical identity. In contrast, combustion of wood, rusting of iron, and burning of paper are all examples of chemical changes. During these processes, the original substances undergo a chemical reaction that transforms them into new substances with different properties. For instance, combusting wood produces ash, carbon dioxide, and other compounds, indicating a change in composition. Rusting involves the oxidation of iron, resulting in iron oxide, while burning paper results in the formation of ash and gases. These transformations reflect the fundamental difference between physical and chemical changes in matter.