Chemistry 162
Exam 1, Feb 1st, 2010
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Exam #1 – Thermodynamics, Gases
SHOW ALL OF YOUR WORK TO RECEIVE
FULL CREDIT
Make a note of the point value of each question, and allocate your time accordingly.
Carefully read each question.
Where appropriate, work must be shown to receive proper credit.
Take your time, make sure to check your work for mistakes when you are finished.
Partial credit will be awarded based on work shown.
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Page
Points
2
30
3
37
4
33
TOTAL
100
Score
1/4
Chemistry 162
Name: ____________________
st
Exam 1, Feb 1 , 2010
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1. (30 points) The following image represents two reactant gases in separate chambers. The valve is
opened allowing a reaction to happen: Nitrogen gas and hydrogen gas react to form ammonia gas. The
reaction goes to completion. Temperature is constant at 295 K.
H2
5.5 Liters
3.1 atm
a.
b.
c.
d.
e.
f.
(2)
(8)
(4)
(4)
(4)
(8)
N2
2.5 Liters
4.3 atm
Balance the equation for this reaction: ___N2(g) + ___H2(g)  ___NH3(g)
How many moles of ammonia gas are produced by the reaction?
How many moles of hydrogen gas remain after the reaction is completed?
How many moles of nitrogen gas remain after the reaction is completed?
What is the final total pressure of the gases in the system?
What are the final partial pressures of each of the gases in the system?
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Chemistry 162
Name: ____________________
st
Exam 1, Feb 1 , 2010
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2. a. (17) I have a 476 gram bar of iron at an initial temperature of 740.8 °C. I drop this iron bar into
1075 grams of water being held in a well-insulated container. The initial temperature of the water was
21.9 °C. What is the temperature of the water when thermal equilibrium is reached?
(Assume that only the water and iron transfer energy). c H 2O  4.184
J
g C
c Fe  0.451
J
g C
b. (5) Draw an energy diagram of this entire process. Clearly state your system.
3. (9) I start with 32147.0 mL of a gas at 65.8 °C and 12.89 atm of pressure. What will the new
volume of this gas be if the temperature and pressure change to 827.5 °C and 945.3 Torr?
4. (3) Circle the state functions.
a) enthalpy b) work
c) temperature d) volume
5. (3) Circle the processes that are endothermic.
a) freezing
b) melting
c) sublimation
d) baking bread
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e) deposition
f) condensation
Chemistry 162
Name: ____________________
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Exam 1, Feb 1 , 2010
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6. a. (14) Zinc and sulfur, when mixed, burn violently in the presence of oxygen:
Zn(s) + ⅛ S8(s) + 2 O2(g) → ZnSO4(s)
Calculate the standard enthalpy change for this reaction, from the following reactions
and subsequent ΔHº values:
2 ZnS(s) + 3 O2(g) → 2 ZnO(s) + 2 SO2(g)
Zn(s) + ⅛ S8(s) → ZnS(s)
ZnO(s) + SO3(g) → ZnSO4(s)
2 SO2(g) + O2(g) → 2 SO3(g)
ΔHº = -927.54 kJ
ΔHº = -183.92 kJ
ΔHº = -230.32 kJ
ΔHº = -196.04 kJ
b. (2) Based on your answer above, is this reaction exothermic, or endothermic? (circle one)
c. (6) Based on your answer above, how much energy is required or released if I react 68.5
grams of solid zinc with excess sulfur and excess oxygen gas?
7. (11) You are given two separate but identical flasks. Flask A contains N2 at 74ºC and 2 atm
pressure. Flask B contains chlorine gas at 74ºC and 1 atm pressure. Compare these two samples (N2
and chlorine gasses) with respect to each of these properties, and briefly explain your answer:
a) Average molecular velocity of each gas
b) Average kinetic energy of each gas
c) The number of molecules of each gas
d) Which flask contains the greater total heat energy (circle one, no explanation needed)
Flask A
Flask B
Same
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