1. Liquids and Solids

3. Phase Changes Solid to Liquid Melting Fusing
Ice melts at 0 degrees Celsius

4. Phase Changes Liquid to gas vaporization Evaporation Boiling
A vapor is the gas phase of a substance that is liquid at room temperature
water boils at 100 degrees Celsius

5. Phase Changes Gas to Liquid Condensation
Water vapor condenses to water liquid at 100 degrees Celsius

6. Phase Changes Liquid to Solid solidification freezing Crystallization
water freezes at 0 degrees Celsius

7. Solid to Gas (skip liquid)
Phase Changes
Solid to Gas (skip liquid)
sublimation
Dry ice (Solid carbon dioxide) sublimes into carbon dioxide gas at room temperature

8. Gas to Solid (skip liquid)
Phase Changes
Gas to Solid (skip liquid)
deposition
Water vapor deposits into ice crystals on cold surfaces

9. Heating Curve

10. Heating Curve of Water

12. Cooling Curve

13. Cooling Curve
gas
condensing
liquid
freezing
solid

14. During a phase change: The temperature does not change (flat line)
Average kinetic energy does not change
Potential Energy changes!

15. KE increases
PE increases

16. Energy equations Q = mcΔt
Can only be used when there is no phase change occurring

17. Energy equations Q = mhf
Can only be used when there is melting or freezing occurring
Hf is the heat of fusion
(Notice there is no temperature term, since temp does not change)

18. Hv is the heat of vaporization
Energy equations
Q = mhv
Can only be used when there is boiling or condensing occurring
Hv is the heat of vaporization
(Notice there is no temperature term, since temp does not change)

19. Example # 1 Which equation would you use for this problem?
How many joules of heat are absorbed when 50 g of water is heated from 30.2 degrees C to 58.6 degrees C?
Q = mcΔt

20. Answer
Q = 50g x 4.18 J/goc x (58.6 – 30.2 oC)
Q = 5936J

21. Example # 2 Which equation would you use for this problem?
How many joules of heat are required to melt 225 g of ice at 0 degrees C?
Q = mHf

22. Answer
Q = 225g x 334 J/g
Q = 75,150 J
Q = kJ

23. Example # 3 Which equation would you use for this problem?
How many joules of heat are required to vaporize 423 g of water at 100 degrees C?
Q = mHv

24. Answer
Q = 423g x 2260 J/g
Q = 955,980 J
Q = kJ

25. Why does boiling 1 g of water require so much more energy than melting 1 g of water?
Boiling = 2260 J/g
Melting = 334 J/g

26. Lots of
energy
needed
to separate
the particles
from liquid to
gas