Document 6525402

Physics 7A SS1, 2007 Final Cover Sheet
INSTRUCTIONS:
Right now, as soon as you get this part of the exam:
1. Fill in this cover sheet completely.
2. Put your name, ID #, first two initials of your last name, and DL section number on each page of the
exam. Look at the chalkboard to get the correct DL Section. This is important!!!! The pages are
separated for grading!
3. Check the exam: there should be 8 problems. Alert a proctor immediately if you do not have a full copy.
Remember:
* You will probably not know the answer or immediately know what to do when you first read a question.
You are being tested on your ability to think. So think about how you can apply the general models and
methods you have learned to the particular situations discussed in the questions. Then do it.
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Name (Print Clearly): Last Student ID Number:___________________________
DL Section Number: first
(This is a number between 1 and 6)
Signature:______________________________________
You may begin the final as soon as you have completed this page, put your name, ID, and DL section number
on each of the following pages.
Useful Information
ΔHmelt(water) = 333.5 kJ/kg
ΔHvap(water) = 2257 kJ/kg
NA= 6.02 x 1023 objects/mole
ΔG = ΔH - TΔS
M(p) = 1.00728u
M(n) = 1.00866u
Matomic(235U)=235.0439u
g = 9.8 m/s2 ≈ 10 m/s2
∆S = Q/T ∆Suniverse ≥ 0
M(e) = 0.00055u
Matomic(98Sr)=97.9285u
kB = 1.38 x 10-23 J/K
R = 8.31 J/mol•K
S = kBln Ω
1 MeV = (1 u) x (931.5)
Matomic(138Xe)=137.9140u
7A Final DL Sec. __Name:
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NOTE: YOU MUST SHOW YOUR WORK AND GIVE CLEAR, CONCISE LOGICAL EXPLANATIONS
(AS NECESSARY) TO RECEIVE CREDIT.
1. (12%)
a) You roll two six-sided dice. The state is the product of the two values you get. What is the number of
microstates for this system and what is the probability of state=6?
b) Using the concept of microstates, explain how the formation of a bond affects the entropy of a system.
2. (12%) Calculate the change in entropy for the reversible freezing of 454 g of water, and plot this to scale on
an appropriate state diagram. Explain how the 2nd Law of Thermodynamics is upheld.
7A Final DL Sec. __Name:
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3. (14%) Heat is added to a sample of 100 ideal gas molecules. The data are summarized in the table.
many modes are active for each molecule? Is this gas monatomic, diatomic, or triatomic?
T(K)
P (105 Pa)
V (10-24 m3)
U (10-21 J)
1246
9.5
0.376
511
1299
9.4
0.610
840
1359
9.5
0.844
1161
7
8
How
4. (12%) For the nuclear reaction, 23592U + (how many?)10n → 9838Sr + 13854Xe, how many neutrons are
needed on the reactants side? Next, show explicitly whether this reaction is endothermic or exothermic by
calculating the energy absorbed or released. Finally, is this nuclear fission or nuclear fusion?
7A Final DL Sec. __Name:
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8.0
A
B
2.0
P (Pa x 105)
5. (12%) An ideal gas undergoes the circular cycle A→B→A as shown in the diagram. What is the sign and
magnitude of the heat for this process? Hint: the area of a circle on a PV diagram is πr1r2, where r1 and r2
are the radii along the P and V axes, respectively.
1.0
3.0
V (m3 x 10-3)
7A Final DL Sec. __Name:
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6. (14%) For the following reaction: 4KClO3(s) → 3KClO4(s) + 1KCl(s), ΔS<0 because the products are
slightly more ordered than the reactants. The bond energy magnitudes of these molecules are:
Eb(KClO3(s))=398 kJ/mol, Eb(KClO4(s))=433 kJ/mol, and Eb(KCl(s))=437 kJ/mol. Is this reaction always
spontaneous, never spontaneous, spontaneous at high temperatures or spontaneous at low temperatures?
(Hint: this reaction takes place at constant T and P.)
7. (12%) At room temperature, 150 unknown ideal gas molecules have a heat capacity of 5.167 x 10-21 J/K.
At a much higher temperature, say T=3000K, would you expect the heat capacity to be larger, smaller, or the
same? Explain your answer.
7A Final DL Sec. __Name:
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first 2 letters of last
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8. (12%) Your Physics 7A professor attaches an ice cube at T=273K and mass 150 g to a horizontal spring so
that the ice cube can slide back and forth across a rough tabletop. The spring constant is 9775 J/m2. The ice
cube is pulled 40 cm from the spring’s equilibrium position (spring stretched) and let go. It travels through
the equilibrium position to 24 cm (spring compressed) before stopping. How much ice melts?