Physical and Chemical Changes - JSS2 Basic science Past Questions and Answers - page 2

A physical change is a type of alteration in which the physical state or appearance of a substance changes without affecting its chemical composition. Examples include changes in shape, size, or state of matter like melting or freezing.

One example of a chemical change is the rusting of iron. When iron reacts with oxygen and moisture in the air, it forms iron oxide, which is a different chemical substance from the original iron.

Physical changes involve alterations in the physical properties of a substance without changing its chemical composition, while chemical changes involve the formation of new substances with different chemical compositions.

Reversibility in changes often depends on the extent to which the original chemical composition is altered. Physical changes, which involve only alterations in physical properties, are often reversible because the original substances remain unchanged. In contrast, chemical changes, which involve the formation of new substances, are usually irreversible because it's difficult or impossible to recover the original reactants.

Chemical changes typically involve the formation of new substances, often with different properties from the original substances. They often involve the breaking and forming of chemical bonds and may release or absorb energy in the form of heat or light.

One example of a physical change involving a phase transition is the melting of ice. When solid ice (water in its solid state) is heated, it undergoes a physical change and transforms into liquid water without changing its chemical composition.