Physical and Chemical Changes

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A physical change is a change in which no new substance is formed. Only physical properties such as state, shape, size, or appearance change. The chemical composition remains the same.

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A chemical change is a permanent change in which a new substance with different properties is formed. The original substance cannot be obtained back by simple physical methods.

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Ice and water have the same chemical composition, H2O. During melting, only the state changes from solid to liquid. No new substance is formed, so it is a physical change.

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Water changes from liquid to solid, but its chemical composition remains H2O. This is a reversible physical change. Equation: Water xrightarrow{freezing} Ice melting [Water, Ice - reversible physical …

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Camphor changes from solid to vapour and then back to solid without forming a new substance. The change is temporary and reversible, so it is a physical change.

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A reversible change is a change that can be reversed by changing the conditions. Water freezing into ice and ice melting into water are reversible changes.

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An irreversible change cannot be brought back to the original state. Burning a piece of paper into ash is an irreversible change.

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Burning paper forms a new substance, ash. Ash cannot be changed back into paper by simple physical methods, so the change is chemical and irreversible.