1. Plan for Fri, 24 Oct 08 Formal report guidelines Quiz 4 returned
Exam 2 review problems
NOTE: I will not check my on Sunday.

2. Quiz 4 Avg: 4.71 +/- 2.64 High: 10, Low: 1
You may re-work Prob. #1 only and turn it in Monday for full credit.
Please staple your new solution to the front of your quiz.
This option is only available to those who attend class Friday, Oct 24th.

3. Which would you guess is in its standard state?
CO2(g) / CO2(s)
H2O(g) / H2O(l) / H2O(s)
N2(g) / N2(l)
Which of the following has DHfo = 0?
CO2(g) / H2O(l) / N2(g)

4. C7H16 (g) + 11 O2 (g)  7 CO2 (g) + 8 H2O (l)
Example
Determine the standard enthalpy change at 25°C for the combustion of one mole of heptane (C7H16) sometimes used in gasoline fuel mixtures. The balanced equation is shown here:
C7H16 (g) + 11 O2 (g)  7 CO2 (g) + 8 H2O (l)
DHfo (kJ/mol)
C7H16(g)
CO2(g)
H2O(l)
ANS: –4,800 kJ

5. DH Stoichiometry Example
When sulfur (S8) burns in air, SO2 is produced. The reaction evolved 9.31 kJ of heat per gram of S8 at constant pressure.
Write the balanced chemical equation, including the appropriate enthalpy change.
How much heat is evolved when 15.0 g of S8 is burned?
5.01 x 103 kJ of heat was evolved from the combustion of S8 in air. How many liters of SO2 were produced if the reaction occurred at 125oC and atm?

6. energy flow Hot water (50oC) Cold water (35oC) 10. g 40. g
Lukewarm water
T = ?? oC
Consider equal masses of hot water and cold water separated by a thermally-conductive barrier inside an insulated box.
The higher temperature on the left indicates that the molecules are, on average, moving more quickly than the molecules on the right. Temperature is a measure of the “vigor” of the random motions of a substance.
CONSERVATION OF ENERGY and THERMAL EQUILIBRIUM:

7. Same gas, different temperatures. B C
Same gas, different temperatures.
Which of curves A, B, and C represents the highest temperature? the lowest? A B C D
Same temperature, different gases.
Curves A-D represent the speed distribution of He, Ne, Ar, and Xe gases at a certain temperature.
Label each curve with the correct noble gas.
= Xe(g)
= Ar(g)
= Ne(g)
= He(g)