1. Happy late bday, Matthew (Sunday)
#5 on “Entropy and Free Energy” sheet from Friday. For the reaction Cl2O(g) + 3/2 O2(g)  2ClO2(g), DS0 = kJ/mol and DH0 = J/molK. At 361oC, what is DG? Is this reaction spontaneous or nonspontaneous? DG=DH-TDS watch your units!

2. #3 and 4 on “Entropy and Free Energy WS”
#3 Increase or decrease in entropy?
Freezing of water (liquid to solid)
2H2(g) + O2(g)  2H2O(g)
2KClO3(s)  2KCl(s) + 3O2(g)

3. #3 and 4 on “Entropy and Free Energy WS”
#4 What are the signs for DH, DS, and D G for the freezing of liquid water at oC?
D H D S D G A B C D

4. Summarizing Favorability and Spontaneity
Sign of ΔS
Sign of ΔH
End Result
+ΔS
(Favorable)
-ΔH
Spontaneous
ΔG < 0
-ΔS
Spontaneous (ΔG < 0)
only at low temperatures
+ΔH
only at high temperature
(unfavorable)
Non-spontaneous
ΔG > 0

5. Items to Bring this Week
Wednesday – 3 pieces of favorite crunchy snack that can burn (cheetos, cheesepuffs are really good)
Friday – ice cream supplies

6. 68 (avg of 10 students above a 17, 7 below 17)
Thermodynamics Quiz
Per
Avg 2 64 3 84 4 63 5
68 (avg of 10 students above a 17, 7 below 17) 6 70

7. Heat Capacities
Does everything heat up and cool down at the same rate?
Different substances have different capacities for storing energy.
It can take 20 minutes to heat water to 75°C. The same mass of any metal might require only 5 minutes.

8. Capacities
Specific heat capacity
Heat capacity
Molar heat capacity

9. Specific Heat
Specific heat is the amount of heat needed to raise the temperature of 1 g of a substance by 1° C.

10. Conductors and Insulators
Conductors are materials that transfer heat easily and quickly. Metals are the best conductors of heat because they have a ___specific heat.
Insulators do not conduct heat easily. They have a ___ specific heat. Examples are water, glass, plastic, rubber and air.
Materials that trap air, such as foam, fur and feathers, and double-paned windows are the best insulators.

11. Conductors and Insulators
Conductors are materials that transfer heat easily and quickly. Metals are the best conductors of heat because they have a low specific heat.
Insulators do not conduct heat easily. They have a high specific heat. Examples are water, glass, plastic, rubber and air.
Materials that trap air, such as foam, fur and feathers, and double-paned windows are the best insulators.

12. Specific heat Q = mcp ΔT Specific Heat can be calculated.
Q is the heat energy (Joules)
m is the mass of the substance (grams)
cp is the specific heat capacity (J/g°C)
ΔT is the change in temperature (°C)
Heat lost = Heat Gained

13. Heat capacity heat capacity for a material, C is calculated
C= heat absorbed/DT = q/DT

14. Molar Heat Capacity molar heat capacity = C/moles q/(mol*DT)
Make the units work and you’ve done the problem right.

15. Properties
Intensive properties not related to the amount of substance.
density, specific heat, temperature
Extensive property - does depend on the amount of stuff.
Heat capacity, mass, heat from a reaction

16. Measuring Energy Changes
Device called calorimeter
Reaction in cup either absorbs or releases energy causing water temp to rise or fall
Temperature change of water tells you whether energy is absorbed or released
Heat lost by substance = heat gained by water

17. Examples
A 46.2 g sample of copper is heated to 95.4ºC and then placed in a calorimeter containing 75.0 g of water at 19.6ºC. The final temperature of both the water and the copper is 21.8ºC. What is the specific heat of copper?