1 .Some materials or objects change when we heat or cool them .

2 .These changes can be reversible {change back } or irreversible { not change back } .

3. when we heat ice cubes they change into water .

4 .How does it changes ?

5 .Is it reversible or irreversible change?

6 .When fire wood burns wood reacts with oxygen producing ash , smoke and carbon dioxide . These new substance cannot be changed back .

7 . This is an irreversible change .

8 . When egg turned into omelette .

9 . Cooking the egg causes a chemical change .

.The proteins in the egg denature and coagulate due to heat forming a solid omelette .

This process cannot be reversed to turn the omelette back into a raw egg .

Example :

When a chocolate bar melts and melting chocolate involves physical change . when heated the chocolate changes from solid to liquid , and when cooled it solid fies again . since no new substance is formed , the process can be reversible .

this is a reversible change .