Physical Properties

Physical properties are ways to describe substances.

ex: bluediameter = 1.0 cmboiling point = 34 degrees C

Physical Changes

… are changes which do not result in a new substance.

Examples: Tearing, chopping, wetting, mixing, cracking, hammering, separating, boiling, freezing, distilling, melting, boiling, subliming,…

Chemical Properties

-- the ability to undergo a chemical change.

Chemical Changes

Things which cause the identity of a substance to change.

Burning, reacting, tarnishing, oxidizing, baking, cooking, decomposing,

How can you tell if a change is Chemical or physical?

• Physical changes are expected… if you add heat and something melts, of course it would melt.

• Chemical changes are unexpected… if you add heat and something solidifies … you wonder if you are going crazy … you aren’t, you just saw a chemical reaction.

What if you don’t know what to expect?

• Chemical changes are difficult or impossible to reverse because the substances obtain new identities as the molecules trade partners (make or break chemical bonds)

• Physical changes are reversible, or at least, don’t result in a new substance – so although it is hard to un-rip paper, you can still use it as paper once you tape it back together.

• In contrast, iron is magnetic when unreacted. Sulfur is a yellow powder. When reacted, a black, non-magnetic substance results.

• If you mix iron and sulfur and don’t react them, the mixture is greyish-yellow, but the iron is still magnetic.