Chemical changes and physical changes are two fundamental types of changes that matter can undergo, and they differ primarily in the following ways:
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Formation of New Substances: Chemical changes result in the formation of new substances with different chemical properties. For example, when iron rusts, it transforms into iron oxide, a new chemical compound. In contrast, physical changes do not produce new substances; they only change the form or appearance of the same substance. For example, melting ice into water does not change the chemical identity of H2O.
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Reversibility: Most physical changes are reversible, meaning the original substance can be recovered. For instance, water can be frozen and then melted back into liquid form. Chemical changes, however, are often irreversible or difficult to reverse since they involve breaking and forming bonds between atoms to create different substances. For example, burning wood creates ash and gases, which cannot easily revert back to their original form.
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Involvement of Heat: While both physical and chemical changes can involve heat, chemical changes typically involve significant changes in energy, often in the form of heat being absorbed or released. For example, combustion reactions usually produce heat. Physical changes might involve heat as well (like melting ice), but the temperature change is generally less significant compared to that in a chemical reaction.
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Phase Changes: Phase changes are usually considered physical changes. When a substance changes from solid to liquid to gas and vice versa, it is undergoing a physical change without altering its chemical composition.
In summary, the main differences are that chemical changes form new substances, are often irreversible, and usually involve significant energy changes, while physical changes do not create new substances and are often reversible. Phase changes are primarily categorized as physical changes.
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