When substances undergo changes, they can be categorized as either physical changes or chemical changes. Physical changes involve alterations in the appearance or state of matter without changing the chemical composition of the substance. For example, when ice melts into water, it is a physical change because the water is still H2O, only the physical appearance of the water changed. Another example is when you crumple a piece of paper - the paper changes its shape but remains paper. On the other hand, chemical changes result in the formation of new substances with entirely different properties than the original substance. One common example is the rusting of iron.

Question

When iron rusts, it combines with oxygen in the air to form a new substance, iron oxide, which has different properties than the original

Answer 1

iron. This process is irreversible under normal conditions, meaning that once iron has rusted, it cannot simply revert back to pure iron without significant intervention. Another classic example of a chemical change is the combustion of wood. When wood burns, it reacts with oxygen to produce ash, carbon dioxide, and water vapor—new substances with different properties from the original wood.

In summary, the key difference between physical and chemical changes lies in whether the chemical composition of the substance is altered. Physical changes affect the form or state but leave the chemical identity intact, while chemical changes result in the creation of new substances with distinct chemical compositions and properties. Understanding these differences is crucial in fields such as chemistry, materials science, and environmental science, where predicting the behavior of substances under various conditions is essential for practical applications.