1. Thermochemistry
Part 2

2. Heat and Changes of State
What are the three states of matter?
What are their changes called?
Did you know?
During a race, an athlete can burn a lot of calories that either do work or are released as heat
The evaporation of sweat from your skin helps to rid your body of excess heat.
HOW?

3. FIVE TYPES of CHANGES Each change s associated with a change in HEAT.
1. Heat of Fusion (solid to liquid)
2. Heat of Solidification (liquid to solid)
3. Heat of Vaporization (liquid to gas)
4. Heat of Condensation (gas to liquid)
5. Heat of Solution (solute dissolves in solvent)

4. 1. Heat of Fusion
What happens if you place an ice cube on a table in a warm room?
The molar heat of fusion (∆Hfus) is the heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature.
Heat is GAINED from
Surroundings.

5. 2. Heat of Solidification
What happens when you put liquid water into a freezer?
The molar heat of solidification (∆Hsolid) is the heat lost when one mole of a liquid solidifies at a constant temperature.
Heat is LOST to
surroundings.

6. Relationship Between Fusion and Solidification
The quantity of heat absorbed by a melting solid is exactly the same as the quantity of heat released when the liquid solidifies; that is, ∆Hfus = –∆Hsolid.
Ice to Liquid ; Liquid to Ice
H2O (s)  H2O (l) ∆Hfus = 6.01 kJ/mol
H2O (l)  H2O (s) ∆Hsolid = kJ/mol
Units: KJ/mol

7. PRACTICE
∆Hfus= 6.01 kJ/mol

8. You do it! We are working backwards in this problem.. PAGE 521 # 21
∆Hfus= 6.01 kJ/mol

9. 3. Heat of Vaporization What happens if we add heat to a pot of water?
The amount of heat necessary to vaporize one mole of a given liquid is called its molar heat of vaporization (∆Hvap).
Heat is GAINED from surroundings.

10. 4. Heat of Condensation
What happens when you take a cold glass of water and place it in a warm room?
The amount of heat released when 1 mol of vapor condenses at the normal boiling point is called its molar heat of condensation (∆Hcond).
Heat is LOST to
surroundings.

11. Relationship between Vaporization and Condensation
The quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses; that is, ∆Hvap = –∆Hcond.
H2O (l)  H2O (g) ∆Hvap = 40.7 kJ/mol
H2O (g)  H2O (l) ∆Hcond = -40.7kJ/mol

12. Practice!
∆Hvap = 40.7 KJ/mol
Ignore the temp and pressure! This is important, but is not required to do calculation!!

13. You try!
Page 524 # 24

14. Some Common Changes in Heat
What is the heat of solidification for ethanol?
What is the heat of condensation for methanol?

15. 5. Heat of Solution
During the formation of a solution, heat is either released or absorbed.
The enthalpy change caused by dissolution of one mole of substance is the molar heat of solution (∆Hsoln).
NH4NO3 dissolved in water becomes cold. So cold, frost will form on outside of container! This is what is in a cold pack.
CaCl2 dissolved in water produces heat. This is what is in a hot pack.

16. Practice!
∆Hsoln = KJ/mol

17. You try!
Page 526 # 26
∆Hsoln = 25.7KJ/mol

18. Homework Study for Test. It is Next Thursday October 2! Problems:
Page 526 #27-31
Page 535 #55
Study the practice
problems we did today!
Study Practice problems
from Notes #5 and previous homework!