CoachA reversible change is a change that can be undone, so that we get back exactly what we started with.
Examples
Example 6.2 (Dissolving and drying)
Sugar stirred into water dissolves. Let the water evaporate, and the sugar comes back: the same sugar, as sweet as before. Dissolving is a reversible change.
Example 6.3 (Ice and water)
An ice cube melts into water on a warm plate; put the water in the freezer and it becomes ice again. Melting and freezing are reversible changes. (Why water melts and freezes is told in the physics book.)
Example 6.4 (Mixing)
Sand mixed with gravel can be sieved apart again; muddy water can be filtered. Mixing is a reversible change: nothing new is made, and the parts can be separated (Chapter 3).