Reversible and Irreversible changes
Reversible changes, like melting and dissolving, can be changed back again.A reversible change might change how a material looks or feels, but it doesn’t create new materials. Some ways to cause reversible changes are:
MELTING: Melted chocolate can be cooled to turn back into a solid.
FREEZING: Water can be frozen to form ice and then heated to turn back into water.
BOILING, EVAPORATING AND CONDENSING: If you capture all the steam that is made when a kettle boils, you can turn it back into water by cooling it.
DISSOLVING: When salt is mixed with water it disappears because it dissolves in the water to make salty water. But we can get the salt back again by boiling off the water. When the water evaporates, the salt will be left behind.
Irreversible changes, like burning, cannot be undone.
In an irreversible change, new materials are always formed. Sometimes these new materials are useful to us. Some ways to cause irreversible change are:
HEATING: For example cooking a raw egg.
MIXING: For example when you mix vinegar and bi-carb, the mixture changes and bubbles of carbon dioxide form. These bubbles and the mixtures cannot be turned back into vinegar and bi-carb.
BURNING: When you burn wood, you get ash and smoke. You can’t turn ash and smoke back into wood.