1. Physical vs. Chemical
Properties and Change

2. Physical Properties
Properties that can be observed or specified without changing substance into another.
Color
Odor
Taste
Size
Density
Physical State
BP and MP

3. Physical Changes Changes in which no new substance is formed
Changes of state
Melting
Boiling
Freezing
Condensation
Sublimation
Sharpening a pencil

4. Physical Changes (cont)
Taking a bite of food
Slicing an onion
Breaking of glass
Etc.

5. Evaporation Some molecules have enough energy to escape the surface
Opposite of condensation
In equilibrium in closed system
In open system will eventually all evaporate because of diffusion in air.
Makes smells possible
No odor without evaporation
Molecules must be at least slightly soluble in water

6. Boiling As temperature of liquid increases:
Vapor pressure of liquid increases
(more molecules have enough energy to escape)
So liquid evaporates faster
When vapor pressure reaches atmospheric pressure:
Liquid boils (bubbles form in the liquid and escape)
Boiling is a cooling process. How?

8. Boiling (cont) Why is boiling point constant?
So you don’t cook things faster by boiling faster.
Only constant at constant atmospheric pressure.
For same reason, melting point is constant
mp doesn’t depend on pressure, why?
Why is boiling with a microwave strange?

9. Chemical Properties Properties exhibited under changes in composition
They describe how a substance can change into other substances
Iron rusts
Baking soda decomposes with heat
Flammability or non-flammability
Wax burns, water doesn’t

10. Chemical Change
A change in which a new substance or substances are formed.
Also called a chemical reaction
Rusting of iron
Digesting food
Burning gasoline or anything
Detonating dynamite
Souring of milk

11. Uses of Chemical and Physical Properties
To separate substances
To identify substances
To distinguish between substances
To predict usefulness of new substances

12. Melting vs. Dissolving
Melting is a change of state involving heat but not a solvent.
Dissolving is a physical change also, but involves a solvent and not necessarily heat

13. H4 – C2
2 - 5, 8, 12, 14, 36, , 54, 61