Plan for Fri, 24 Oct 08

1
Plan for Fri, 24 Oct 08

• Formal report guidelines
• Quiz 4 returned
• Exam 2 review problems
• NOTE I will not check my email 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
Example
Determine the standard enthalpy change at 25C
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) -264 CO2(g)
-394 H2O(l) -286
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 0.879 atm?

6
Cold water (35oC) 40. g
Hot water (50oC) 10. g
energy flow
Lukewarm water T ?? oC
7
Same gas, different temperatures. Which of curves
A, B, and C represents the highest temperature?
the lowest?
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)