Chemical Change:

A chemical change refers to a process in which one or more substances are transformed into new substances with different chemical properties. It involves the breaking and formation of chemical bonds, resulting in a rearrangement of atoms. Chemical changes are typically irreversible, meaning it is difficult or impossible to revert the substances back to their original form.

Examples of Chemical Changes:
1. Combustion: When wood burns, it undergoes a chemical change, producing ash, smoke, and heat.
2. Oxidation: When iron rusts, it combines with oxygen from the air to form iron oxide, altering its chemical composition.
3. Digestion: The breakdown of food in our bodies involves various chemical reactions that transform complex molecules into simpler ones.

Physical Change:

A physical change, on the other hand, refers to a process in which the substance undergoes a change in its physical appearance or phase without altering its chemical composition. Physical changes are generally reversible, and the original substance can be recovered.

Examples of Physical Changes:
1. Melting: When ice melts, it changes from a solid to a liquid state without any alteration in its chemical composition.
2. Boiling: Heating water causes it to change from a liquid to a gaseous state, but the chemical composition remains the same.
3. Dissolving: When sugar dissolves in water, it forms a homogeneous mixture, but there is no change in the chemical properties of either substance.

Differences between Chemical and Physical Changes:

1. Composition: Chemical changes involve the formation of new substances with different chemical compositions, while physical changes do not alter the composition.
2. Reversibility: Chemical changes are generally irreversible, whereas physical changes can usually be reversed, recovering the original substance.
3. Energy: Chemical changes often involve the release or absorption of energy in the form of heat, light, or sound, while physical changes usually do not.
4. Particle Arrangement: Chemical changes involve the rearrangement of atoms and molecules, whereas physical changes only affect the arrangement or state of the particles.
5. Observability: Physical changes can often be observed without the need for chemical tests, while chemical changes may require specific tests or indicators to identify the transformation.

In summary, chemical changes result in the formation of new substances with different properties and are typically irreversible, while physical changes only affect the physical appearance or state of a substance and are generally reversible.