Physical Changes vs. Chemical Changes

Key Differences

• Physical Change: Chemical identity of the substance remains the same.
• Chemical Change: Chemical identity of the substance changes, leading to a new chemical formula.

Examples of Physical Changes

• Crumpling Paper: Remains paper, no change in identity.
• Freezing Water: Water (H2O) remains the same, only changes from liquid to solid.
• Boiling Water: Liquid water becomes steam (H2O), maintaining chemical identity.
• Melting Ice: Solid to liquid water, remains H2O.
• Vaporization: Liquid to gas; e.g., boiling water to steam.
• Condensation: Gas to liquid, e.g., steam turning back to water.
• Sublimation: Solid directly to gas; e.g., dry ice (CO2) sublimates.
• Deposition: Gas directly to solid; e.g., CO2 gas to dry ice.
• Ductility of Metals: Copper wire drawing, the metal remains copper.
• Malleability of Metals: Hammering metals into sheets.

Examples of Chemical Changes

• Burning Paper: Transforms to carbon dioxide and water vapor.
• Electrolysis of Water: Breaks water into hydrogen and oxygen gases.
• Burning Gasoline: Reacts with oxygen to form carbon dioxide and water.
• Rusting of Iron: Iron reacts with oxygen to form iron oxide.
• Color Change in Solutions: Often indicates a chemical reaction.
• Corrosion by Acid: Metal reacting with acid, e.g., zinc with acid.
• Silver Tarnishing: Silver reacts with sulfur forming silver sulfide, turning black.

Important Concepts

• Burning: Always a chemical change (new substances formed).
• Corrosion: Always a chemical change (new substances formed).
• Color Change: Typically indicates a chemical change due to a reaction.
• Phase Changes: Such as freezing, melting, boiling, etc., are physical changes.