Burning of candle wick is an example of chemical change as wick get burns and new substance is formed with a new property.

In a chemical change, the molecules of a substance do change. This means that the arrangement and composition of the atoms within the molecules are altered, resulting in the formation of new substances with different properties. This is in contrast to a physical change, where the molecules remain the same and only the physical state or arrangement of the substance is altered.

Explanation:

Molecule of substance change:
During a chemical change, the bonds between atoms in the molecules are broken and new bonds are formed to create different molecules. This rearrangement of atoms leads to the formation of new substances with unique properties. For example, when wood is burned, its molecules undergo a chemical change and are converted into carbon dioxide and water vapor.

Examples of chemical changes:
1. Rusting of iron: When iron reacts with oxygen and moisture in the air, it undergoes a chemical change to form iron oxide, commonly known as rust.
2. Digestion of food: The process of digestion involves the breakdown of complex molecules, such as carbohydrates, proteins, and fats, into simpler molecules that can be absorbed by the body. This is a chemical change that occurs in our digestive system.
3. Combustion of fuel: When a fuel, such as gasoline or natural gas, is burned, it undergoes a chemical change to produce carbon dioxide and water vapor, releasing energy in the form of heat and light.

Difference between chemical and physical changes:
- In a physical change, the molecules of a substance do not change, whereas in a chemical change, the molecules do change.
- Physical changes are usually reversible, meaning the substance can return to its original state, while chemical changes are often irreversible.
- Physical changes only affect the physical properties of a substance, such as its shape, size, or state of matter, while chemical changes alter the chemical properties of a substance, such as its ability to react with other substances or its composition.

Conclusion:

In summary, a chemical change involves the transformation of molecules in a substance, resulting in the formation of new substances with different properties. This process is irreversible and distinct from physical changes, which only affect the physical properties of a substance.