1. Topic: Heating/Cooling Curves (energy/phase changes) Do Now: Water boils at _____torr, ____1atm, _______mm Hg, ______kPa

2. Review: Name the phase change S  L L  G G  L L  S S  G G  S Melting (fusion) Boiling (vaporization) condensation Freezing (solidification) sublimation deposition

3. REVIEW: 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 shortly)

4. As you go from S  L  G, you are increasing the distance between molecules, so you are increasing their PE (click) !PE We can see these energy changes by looking at a heat/cooling curve – next slide PE Solid Liquid Gas Endothermic Exothermic Sublimation Vaporization (boiling) Melting (fusion) Deposition Condensation Freezing (solidification)

5. B D  E C  B E  D MELTING Vaporization (boiling) FREEZING Condensation EXO ENDO

6. Which phase changes absorb energy (endothermic)? Which phase changes release energy (exothermic)? Melting, Boiling (vaporization) FreezingCondensation Freezing, Condensation

8. TURN TO PACKET page 13, take notes here:

9. Time Temperature I II IIIIVV Solid Solid & Liquid Liquid Liquid & Gas Gas K.E.  K.E.↔ P.E.↔ P.E.  Melt pt. Boil pt. ● ●

10. Melting Point is temp at which liquid & solid phases of substance coexist at equilibrium higher the mp, the stronger the IMF Lets check it out: http://www.harcourtschool.com/activity/hot plate/index.html http://www.harcourtschool.com/activity/hot plate/index.html

11. Freezing Point Temp at which liquid is converted to crystalline solid How does fp compare to mp? They’re the same: for H 2 O = 0˚C

12. Time Temperature I II IIIIVV Solid Solid & Liquid Liquid Liquid & Gas Gas K.E.  K.E.↔ P.E.↔ P.E.  Melt pt. Boil pt. ● ● Freezing pt. ●

13. B D  E C  B E  D MELTING Vaporization (boiling) FREEZING Condensation Melting point/Freezing Point Boiling Point

14. Melting & Boiling Points (start of the phase change) Plateaus = Phase changes = PE changes –always given as temp (˚C, K) WHY IS IT CALLED A POINT?

15. 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

16. QUICK QUESTION: What happens to temperature as heat is added to boiling water? Nothing, temp doesn't’t change b/c 2 phases are present –  temp will change when only 1 phase is present!

17. PAGE 13 answer 3-8 3. MP = _________ BP=_______ 7. When is the kinetic energy of the sample the greatest? 8. Given a constant heating rate of 150 Joules per minute, how many joules of heat must the sample absorb to melt all of the sample? To vaporize all of the sample? GAS phase 150 J9 minutes= 1350 Joules minute 150 J30 minutes= 4500 Joules minute 9 30 70 °C 150 °C

18. What do you think a cooling curve would look like?

19. Potential Energy Energy of relative position This position is important b/c molecules are always attracted to one another How close they are to one another affects how much energy is needed to be put into system to pull molecules apart from one another the farther apart, the higher their PE BACK