Physical changes
Physical changes are changes that do not affect the chemical composition of a substance. No new product is formed during physical change. Physical changes are concerned with energy and states of matter. Many physical changes are reversible using physical means. For example, salt dissolved in water can be recovered by boiling the water allowing it to evaporate. Physical properties change during physical change. For example, color, shape, size, volume, durability.
Examples:
Melting of ice
Breaking of wire into pieces
Dissolving sugar in water
Freezing water to make ice
Cutting paper into pieces
Chemical changes
During chemical change a new substance is formed. The composition of a substance changes during chemical change. During chemical change one substance combines with another to form a new substance, or, decomposes into new substances. Chemical reactions lead to chemical changes which are not reversible except by further chemical reaction.
Examples:
Cooking
Burning fuel
Rusting of iron
Digesting food
Mixing acid and base
How to differentiate between physical change and chemical change?
A chemical change makes a substance that was not there before. A chemical change may be accompanied by light, heat, color change, gas production, odor, or sound which hints that a chemical change took place. The starting and ending substances of a physical change are the same, even though they may look different.
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