1. October 24
Objectives
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 Hfus and Hvap from the heating curves
Cooling curves

2. States of Matter

3. States of Matter .

4. 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 rise during the phase change.

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

6. Endothermic Phase Changes
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.

7. 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.

8. 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!!!

9. Problems
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 C ?

10. 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

13. 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.

15. October 21
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 0C to 100 0C
2.-How much heat is needed to completely vaporize 200 g of water at 100 0C

16. q (amount of heat ) table T
q = m C D T

17. Heat of Fusion Hfus
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 Hfus

18. 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 Hvap