da answer:
1. Definition: Physical changes are changes in the physical properties of a substance, such as shape, size, or state, without changing its chemical composition. For example, melting ice into water is a physical change. On the other hand, chemical changes involve the formation of new substances with different chemical properties. For instance, when wood burns, it undergoes a chemical change and turns into ash and smoke.
2. Reversibility: Physical changes are generally reversible, meaning the substance can return to its original state. For example, if you freeze water, it becomes ice, but if you warm it up again, it will return to its liquid state. Chemical changes, however, are often irreversible. Once a chemical reaction occurs, it is difficult or impossible to reverse it and retrieve the original substances.
3. Energy Change: Physical changes usually do not involve a significant energy change. Energy may be absorbed or released during a physical change, but the overall amount of energy remains the same. For example, when water boils, it absorbs heat energy from the surroundings. In contrast, chemical changes often involve a noticeable energy change. Some chemical reactions release energy, such as burning wood, while others absorb energy, like photosynthesis.
4. Composition: Physical changes do not alter the composition of a substance. The molecules or atoms that make up the substance remain the same. For example, when you crush a can, its shape changes, but the composition of the metal remains unchanged. Chemical changes, however, result in a new composition. Bonds between atoms are broken and new bonds are formed, leading to the creation of different substances. For instance, when iron rusts, it reacts with oxygen in the air to form iron oxide, altering its composition.
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