1. October 22  Objective  To represent the changes of energy that occur while a substance is being heated.

2. Do now!  How much heat is needed to completely melt 10 g of ice at 0 0 C ?  How much heat is needed to vaporize 10 g of water at 100 0 C ?

3. Calorimetry problems- review questions 7. 2 (172 J/g) 8. 4 (53,800J) 13. 1.2 C 14. 50.1 kJ 15. 226.0 kJ 16. 2260. J 17. 1380 J/g

4. States of Matter

5. .

6. Energy Changes Associated with Changes of State  The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other.  The temperature of the substance does not change during a phase change !!!

7. October 23 Objective: How to calculate heat from heating curves Do now: Draw a heating curve for the heating of 2 grams of substance that are being heated at a rate of 50 J/min. Melting Point 20 C Boiling Point 80 C Substance begins to melt at minute 2 and melts for 1 minute. It begins to boil at minute 8 and it takes 3 minutes to completely boil.

8. Set 2 – Heat Answers  13 3  14 4  15 4  16 3  17 3  18 2  19 2  20 3  21 122J/g x 7.5 g= 915 J

9. MC answers 1) 2 2) 1 3) 2 4) 3 5) 4 6) 3 7) 1 8) 4 9) 4 10) 4 * more about this topic next week 11) 4 12) 4 13) 3 14) 2 15) 1

10. Heating curve 1) 20 C 2) B and d 3) KE (temperature) remains constant PE increases 3) S and L 4) 20 C 5) 60 C 6) GasT 7) Increases (is T!) 8) E 9) 20minx100J/min=2000J 2000J/20 g = 100J/g 10) 1000J/20 g = 50 J/g 11) 60 C

11.  Types of energy  POTENTIAL ENERGY :  STORED ENERGY. The energy inside the substance.  KINETIC ENERGY : Associated with motion.  Average KE = TEMPERATURE

12.  If the substance is melting or boiling, heat is being absorbed, and is being used to change the state of matter.  THE AVERAGE KINETIC ENERGY DOES NOT CHANGE!!! THE POTENTIAL ENERGY INCREASES. Endothermic Phase Changes

13. Melting Point and Freezing Point  The temperature at which a substance melts. Is the same temperature at which the substance freeze.  Boiling Point and Condensation Point are the same temperature.  Normal boiling point is the temperature at which a liquid boils at normal pressure.

14. Exothermic changes  If the substance is undergoing condensation or freezing then heat energy is being released. The potential energy is decreasing and the TEMPERATURE REMAINS CONSTANT!!!

15. VAPORIZATION IS ENDOTHERMIC  In hot climates drinking water is cooled by evaporating water from the surfaces of porous clay pots. As water evaporates it ABSORBS heat from the water inside the container which is maintained cool.  Like cooling yourself off on a hot day by pouring water over your body. As water evaporates it absorbs heat

18. FREEZING IS EXOTHERMIC  In freezing weather, citrus crops are sprayed with water to protect the fruit from frost damage. As the water freezes (around the fruit-outside the fruit!) it releases heat, which helps to prevent the fruit from freezing.

20. October 23  How to calculate the amount of heat that a substance absorbs while it is being heated up.  DO NOW  1.-Calculate the amount of heat needed to increase the temperature of 200g of water from 0 0 C to 100 0 C. The heating rate is 100J/min.  2.-How much heat is needed to completely vaporize 200 g of water at 100 0 C

21.  q (amount of heat ) table T  q = m C  T

22. Heat of Fusion  H fus Amount of heat needed to completely melt 1 gram of substance at its melting point. At the melting point the heat is calculated Heat = mass x H fus

23. Heat of Vaporization Amount of heat needed to completely boil off 1 gram of substance at its boiling point. At the boiling point the heat is calculated Heat = mass x H vap

24.  Describe what happens with PE and KE as phase changes  Identify MP and BP from heating curve  MP=FP and PB=condensation point  Define heat of fusion and heat of vaporization  Calculate the H fus and H vap from the heating curves  Cooling curves