1. Do Now & Announcements Work on Phase diagram practice
Unit 5 Quest TUES 10/20
Midterm FRI 10/23 (we will review Tues, Wed, and Thurs)

3. Definitions
Kinetic Energy=the energy associated with moving particles (i.e. atoms)
Temperature=measure of the average kinetic energy of a sample of a substance.
Heat=is measured as the energy that is transferred from one object to another because of a difference in temperature. The direction of heat flow is always from the hotter object to the colder object.

4. Demo

5. Specific Heat Capacity: The amount of energy needed to raise the temperature of 1 gram of a substance by 1°C
Heat = Energy transferred due to a difference in temperatures. The amount of heat absorbed or released in a physical or chemical reaction can be calculated using the equation q = mCΔT

6. Example
How much heat is required to raise the temperature of 5 grams of water from 20°C to 100°C? The specific heat of water is 4.18 J/g°C.

7. Answer practice questions

8. Answer questions 1-7 based on the “Heating Curve”

9. 1. During which 3 line segments does the temperature of the substance increase?
2. During which 2 line segments does the temperature of the substance remain the same?
3. At which point do the molecules of the substance have the lowest average kinetic energy? The highest?
  AB, CD, and EF
BC and DE
Lowest average KE: A
Highest average KE: F

10. 4. Which phases of matter are present during segment BC?
5. Which phases of matter are present during segment DE?
6. Even though heat is being added to the substance the entire time, why do you think there is no change in temperature during segments BC and DE? Where do you think the heat energy is going or being used for?   
7. Comparing segments B–C and D–E, what information is conveyed by the observation that segment D–E is longer?
Solid and liquid
Liquid and gas
The heat is being used to melt the substance (BC) or boil it (DE)
It takes more heat energy to boil the substance than it does to melt it

11. Kinetic vs. Potential Energy
Kinetic Energy=the energy associated with moving particles; related to temperature.
Potential Energy=the energy associated with the spaces between the atoms It is NOT related to temperature; it is related with phase change

12. *Heat energy is being transferred to either KE or PE
*When KE is changing, PE remains constant
*When PE is changing, KE remains constant ↑ ↑
None
(molecules still pretty close together)
None
None ↑
(Molecules are getting further apart as solid changes into liquid)
None ↑ ↑
(molecules still loosely together)
None
None ↑
(Molecules are getting further apart as liquid changes into gas) ↑ ↑
None
(molecules still far apart)

13. gas
condensation
liquid
freezing
solid
We can also apply the same concepts to a cooling curve, in which a substance is cooled (or heat is removed from a substance) over time. ↓ ↓
None
(molecules still far apart)
None
None ↓
(Molecules are getting closer together as gas changes into liquid) ↓ ↓
None
(molecules still loosely together) ↓
(Molecules are getting closer together as liquid changes into solid)
None
None ↓ ↓
None
(molecules still pretty close together)

14. Why can’t we use this formula when there is a phase change
Why can’t we use this formula when there is a phase change? Consider the problem “how many joules are required to melt 100 grams of ice at 0°C?”
If we actually tried to use q=mCΔT to solve this problem…
q = 100 g x 4.18 J/g°C x 0°C
q = 0 Joules….
But we know that you need heat energy to melt something…!

15. Heat of Fusion: amount of heat energy required to change a substance from a solid to a liquid; Heat energy required to melt a substance: q=mHf
Note: The amount of energy released when a substance changes from liquid to solid is equal to the Heat of Fusion
q=mHf
q=-mHf

16. Heat of Vaporization: amount of heat energy required to change a substance from a liquid to a gas; heat energy required to boil a substance: q=mHv
Note: the amount of energy released when a substance changes from a gas to a liquid is equal to the Heat of Vaporization
q=mHv
q=-mHv

17. q=mHf and q=mHv Problems:
1. How many joules are required to melt 100 grams of ice at 0°C? The heat of fusion for water is 334 J/g q= m= Hf =
q = 100 g x 334 J/g
100 g
q = 33,400 J
334 J/g

18. How many joules are absorbed by a 50 gram sample of H2O that is boiling? The heat of vaporization of water is 2260 J/g q= m=
Hv =
q = 50 g x 2260 J/g
50 g
2260 J/g
q = 113,000 J