Heating & Cooling Curves

Do Now: Name the phase changeS LL GG LL SS GG S

Melting (fusion)

Boiling (vaporization)condensation

Freezing (solidification)

sublimation

deposition

All Phase changes accompanied by energy changes

• Phase changes are physical changes:– sometimes energy is absorbed (endothermic)

– sometimes energy is released (exothermic)

• Energy change for given phase change can be measured/calculated (we’re going to learn how to do this tomorrow)

• As you go from S L G, you are increasing the distance between molecules, so you are increasing their PE !

We can see these energy changes by looking at a heat/cooling curve – next slide

PE

Solid

Liquid

Gas

Endothermic

Exothermic

Sublimation

Vaporization

Melting (fusion)

Deposition

Condensation

Freezing (solidification)

TURN TO PACKET page 11, take notes here:

Time

Tem

pera

ture

I II III IV V

Solid

Solid & Liquid

Liquid

Liquid & Gas

Gas

K.E.

K.E. K.E.K.E.↔

K.E.↔P.E.↔ P.E.

↔P.E.↔

P.E. P.E.

Melt pt.

Boil pt.

●

●

During Phase changes

• More than one phase is present– Melting : solid and liquid

– Boiling: liquid and gas

(lets check out a tiger animation)

• temperature is constant: T=0–There is no change in temp!!!!!

***NOTE: if 2 phases are present, temp is constant

Melting & Boiling Points

• Plateaus = Phase changes = PE changes

– always given as temp (˚C, K)

• WHY IS IT CALLED A POINT?

QUICK QUESTION:What happens to temperature as

heat is added at boiling point?

• Nothing, temp doesn't’t change until only 1 phase is present!

What do you think a cooling curve would look like?