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. A word to the wise... We automatically report anyone suspected of cheating to Student Judicial Affairs. I certify by my signature below that I have read the above instructions and that I will abide by the UC Davis Code of Academic Conduct. This includes • not copying from anyone else’s final • not letting any other student copy from my final • not discussing this final exam with any student who has not yet taken it, nor providing any information, written or oral, that might get to a student who has not yet taken it. 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: ___________________ ________________ first 2 letters of last last first 1 2 3 4 5 6 7 8 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: ___________________ ________________ first 2 letters of last last first 1 2 3 4 5 6 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: ___________________ ________________ first 2 letters of last last first 1 2 3 4 5 6 7 8 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: ___________________ ________________ first 2 letters of last last first 1 2 3 4 5 6 7 8 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: ___________________ ________________ first 2 letters of last last first 1 2 3 4 5 6 7 8 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?