Chemistry 3501/5501 Sample Exam II November 8, 2010 1) Fill in the correct answer, by letter, on the Scantron form. 2) There is one correct answer to every multiple-choice problem. There is no partial credit. There is no penalty for guessing. 3) A list of useful formulae and other data is provided at the end of the exam. No electronic devices of any sort are allowed. 4) You should try to go through all the problems once quickly, saving harder ones for later. 5) There are 20 problems. Each is worth 5 points. 6) Upon leaving, turn in your Scantron form. Be sure to put your name and student id on the Scantron form. You may take the exam questions with you for reference in determining your score upon posting of the answer key. This is a Sample Exam — Only 6 problems are listed. 1. What are the natural independent variables of the enthalpy, H? (a) (b) (c) P and V P and T P and S 2. You have NA molecules each with a degeneracy of 2 in its lowest energy state. What is the entropy of this system at 0 K? (a) (b) (c) 0 2R ln NA R ln (2NA) 3. Consider the following exothermic chemical reaction (d) (e) (f) (d) (e) (f) P and U S and U S and V R ln 2 NAR ln 2 kB ln (2NA) H2(g) + Cl2(g)  2HCl(g) where the constant pressure heat capacities for H2, Cl2, and HCl are 29, 34, and 29 J mol–1 K–1, respectively (independent of temperature). If the temperature is increased from 100 to 200 K, how will the enthalpy of reaction change? (d) (e) (f) 5 kJ mol–1 more exothermic 5 kJ mol–1 more exothermic none of the above (a) (b) (c) It will not change 0.5 kJ mol–1 more exothermic 0.5 kJ mol–1 less exothermic 4. You have a gas that has a temperature dependent constant pressure molar heat capacity given by CP(T) = ( 10 – 0.02T ) R What is the change in molar enthalpy of the gas if you raise the temperature from 100 K to 200 K (with no phase transitions; all values times 1 K for unit purposes)? (a) (b) (c) 0R R 10 R (d) (e) (f) 500 R 700 R 1000 R 5. From the Maxwell relations, one may derive ⎛ ∂H ⎞ ⎛ ∂V ⎞ ⎜ ⎟ = V − T ⎜ ⎟ ⎝ ∂P ⎠T ⎝ ∂T ⎠P What is the correct expression for the pressure derivative of the enthalpy at constant temperature for a gas that obeys the equation of state € PV = RT + B(T)P? (a) (b) € (c) ⎛ dB ⎞ V − T ⎜ ⎟ ⎝ dT ⎠ ⎛ dB ⎞ B(T ) − T ⎜ ⎟ ⎝ dT ⎠ RT RT ⎛ dB ⎞ − ⎜ ⎟ P P ⎝ dT ⎠ € € (d) RT − TB(T ) P (e) RT RT ⎛ dB ⎞ B(T ) − ⎜ ⎟ P P ⎝ dT ⎠ (f) 0 € € 6. (a) (b) (c) For an adiabatic expansion of a gas, which of the following is always true? q=0 w=0 ΔU = 0 (d) (e) (f) ΔU = w (b) and (c) (a) and (d)