The difference between chemical and physical changes lies primarily in whether the substance's chemical identity is altered.

Physical Change

• Involves changes in the size, shape, or state of a substance without changing its chemical composition.
• No new substances are formed.
• Generally reversible processes (e.g., melting, freezing, condensation).
• Examples: melting ice into water, tearing paper, dissolving sugar in water, boiling water, stretching a rubber band.
• Physical changes affect physical properties like color, texture, shape, and state but do not affect chemical properties.
• No breaking or forming of chemical bonds occurs.
• Usually does not involve energy release or absorption, or if it does, it is minimal and reversible

Chemical Change

• Involves a change at the molecular level resulting in the formation of one or more new substances with different chemical properties.
• Chemical bonds are broken and new bonds are formed.
• Changes are generally irreversible.
• Often accompanied by observable signs such as temperature change, color change, gas production, odor change, or precipitate formation.
• Examples: burning wood, rusting iron, cooking an egg, digestion, fermentation, baking a cake.
• Chemical changes involve energy changes, either releasing or absorbing heat or light.
• The original substances lose their chemical properties and new substances with distinct properties are formed

Summary Table

Aspect| Physical Change| Chemical Change
---|---|---
Substance identity| Remains the same| Changes, new substances formed
Reversibility| Usually reversible| Usually irreversible
Bond breaking/forming| No| Yes
Energy change| Minimal or none| Often significant (heat, light, sound)
Examples| Melting ice, tearing paper, dissolving sugar| Burning wood, rusting iron, cooking egg
Observable signs| Change in state, shape, size, color| Color change, gas release, temperature change, odor change, precipitate formation

In essence, physical changes alter the form or appearance of a substance without changing its chemical nature, whereas chemical changes transform substances into entirely new materials with different chemical identities