Differentiate between physical and chemical changes. Give two examples of each, explaining why they are classified as such.

A physical change is a change in the form or appearance of a substance, but not in its chemical composition. No new substance is formed, and the change is often reversible. Examples: 

1. Melting of ice: Ice (solid water) changes to liquid water, but it's still H₂O. No new substance is formed. 
2. Dissolving sugar in water: Sugar molecules are dispersed in water, but their chemical identity remains the same. 

A chemical change (or chemical reaction) results in the formation of new substances with different chemical properties. It is usually irreversible. 

Examples: 

1. Burning of wood: Wood combines with oxygen to produce ash, carbon dioxide, and water vapor, all new substances. 
2. Rusting of iron: Iron reacts with oxygen and water to form iron oxide (rust), a new substance with different properties.