Reversible changes and Irreversible changesAll changes in the world are one of the two types – Reversible changes and irreversible changes. A change which can happen backwards, that is, can be reversed is called a reversible change. If you keep water in the freezer for some time, it transforms into ice. But as soon as you take it out of the freezer, it turns into water again. This is a reversible change. Similarly, if you boil water, it evaporates and becomes water vapour. When you cool this vapour down, it turns back to water.A change which cannot happen backwards, that is, it cannot be reversed is called an irreversible change. When you burn a piece of paper, it turns to ash. It cannot become paper again. Your height cannot decrease. These are irreversible changes. They cannot be reversed at all.physical changes and chemical changes are.Physical changes are changes that occur in the physical properties of the substance, like shape, size and nature. Physical changes may or may not be reversible changes. Like, turning of water into ice is an example of reversible changes but growth in height is an irreversible change.Chemical changes are changes that occur in the chemical properties of the substance like its flammability, radioactivity, etc. All chemical changes are irreversible changes. Once the chemical properties of a substance are changed, it becomes another substance. Thus, it cannot return to its original state.