How are physical and chemical changes different?
Physical changes are those changes in which the phase of the substance may change. This change can be generally observed (especially if it is a phase change). However, there is no change in the composition of the material, that is the starting and ending material is the same. For example, melting of a metal (Say iron or copper) is a physical change, since the state (or phase) has changed. However, the final product is still the same metal (iron or copper, etc.).
In comparison, chemical changes involve a change in the composition of the material. Such changes may be observed through a release of gases, change in color, etc. An example is the rusting of iron. Over time, the pure metal gets oxidized and we see a color change, which is a visual confirmation of oxidation reaction (in this case) and a chemical change.
Hope this helps.
Chemical changes are changes that result in the formation of a new substance. In other words, the composition of a substance changes when the substance undergoes a chemical change. Chemical reactions are chemical changes. Examples of chemical changes (and reactions) are combustion, decomposition, fermentation, and oxidation. Color changes, bubbles, and the formation of a precipitate are often indicators that a chemical change has occurred.
The composition of a substance does not change during physical change, but physical changes may result in a change of the form, appearance, shape, or size of a substance. All phase changes are physical changes. Other examples of physical changes include snapping, smashing, cracking, stretching, cutting, and dissolving.