Chemical or Physical Change?

Physical ChangeChemical before change is the same chemical

afterwards.

• Only its form has been altered.

• Examples:

• Big piece broken into smaller pieces

• Phase changes

• Shape change: bending a straw

Chemical ChangeChemical before change is not the same chemical after.Change in Properties:• Melting point, boiling points, density, color, taste, texture,

smell, etc. are now different.• Precipitation: solid forms when 2 liquids react when mixed• Gas production: Change in Energy:• Heat energy absorbed, heat energy released, light energy

released

Chemical or Physical Change?

Cutting paper?

PhysicalWhy?Paper beforePaper afterOnly altered its form.

Chemical or Physical Change?Ice melting?

PhysicalWhy?Water before, water after.

Just a phase change, solid -> liquid

Chemical or Physical Change?

Toast burning?ChemicalWhy?Change in properties.

Different smell, taste, color, texture.

Chemical or Physical Change?

Rocket fuel burning?

chemical

Why?Heat and light energy

released

Gas production

Chemical or Physical Change?Sawing wood?PhysicalWhy?Wood before, wood after,

just smaller pieces.

Chemical or Physical Change?

Metal rusting?chemicalWhy?Metal before, rust (iron

oxide) after

Color change (grey to red/orange),

strength change (strong to weak)

texture (smooth to powdery)

Chemical or Physical Change?Disappearing puddle?

Physical

Why?

Water before, water afterJust a phase change:

Liquid water to gaseous water

Chemical or Physical Change?Candle burning?ChemicalWhy?Change in energy: release of

light and heat energyWax reacts with oxygen in air and

produces carbon dioxide gas and water gas

Chemical or Physical Change?

Dry ice?PhysicalWhy?Carbon dioxide before, carbon

dioxide after

Phase change:

Solid to gas (sublimation)