Page 1. N A = x mol -1 R = mmhg = 1 h = x J s c = 3.00 x 10 8 m/s L atm

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1 Page 1 Practice for Exam 3. Note: Many if not most of the questions below appeared on a past exam, but not necessarily on the same exam. I've also combined problems from at least two past exams onto this exam, so that is why the numbering is all crazy (I've added A's, B's, and C's to differentiate the different "topics" (each from a different past exam); be careful not to get them mixed up when you look at the answer keys!). I have not taken pains to make sure all topics are equally represented on this practice exam, so as usual, remember to use your problem sets and worksheets as the ultimate guide as to what topics and problem types are fair game on the exam you will actually take. The following information (and maybe other things) will be provided on the first page of the exam: J x 10 J s water E 2 g C n n J = 1 cal N A = x mol -1 R = mmhg = 1 h = x J s c = 3.00 x 10 8 m/s L atm mol K atm (exact) Section A-Gases 1A. Circle the correct answer (18 pts total) (2 points each) (b) If a sample of gas is warmed in a rigid container (i.e., with fixed volume), which is true? i) the density of the gas remains the same ii) the pressure of the gas increases iii) the average distance between the gas particles remains the same iv) all of the above 2A. Write T (True) or F (False) for the following statements. If the statement is false correct it by changing, dropping, or adding a few words (6 points) c) For a fixed number of moles of an ideal gas at a constant temperature, when the pressure increases the volume will decrease and the molecular speed will increase. d) Gases are easier to compress than liquids because there is much more space between particles in a gas than in a liquid. Free Response Questions--A 7A. (8 pts) A box of fixed volume contains two gases inside, A and B, at 35 C. Assuming the data in the plots are corrrect, state whether each statement below is true (T) or false (F). You do NOT need to correct it if it is false here!! (a) The particles of A have a greater average speed than those of B. (b) The partial pressure of A is greater than the partial pressure of B. (c) The molar mass of A is greater than the molar mass of B. (d) The particles of A have a greater average kinetic energy than # p a r t i c l e s A B T = 35 C

2 Page 2 the particles of B. speed 10A. (11 pts) (a) (7 pts) One industrial process for the removal of hydrogen sulfide from natural gas is its reaction with sulfur dioxide: 2 H 2 S(g) + SO 2 (g) 3 S(s) + 2 H 2 O(g) What volume of SO 2 at 5.0 atm and 252 C will be used up in the production of 21 mol of S(s)? (b) (4 pts) (not related to part (a) at all) A sample of a gas has a volume of 27.3 L at 134 K and 1.0 atm pressure. What will be the volume if the temperature becomes 222 K and the pressure becomes 2.5 atm? Section B-Thermochemistry 1B. Circle the correct answer (12 pts total) (2 points each) (b) Which of the following equations represents a process for which H > 0? i) CH 3 OH(g) CH 3 OH(l) ii) I 2 (s) I 2 (g) iii) C(g) + O(g) CO(g) iv) All of the above v) None of the above (c) The reaction represented by the following equation will be: Cl-Br + Cl-Br Cl-Cl + Br-Br i) exothermic if the bonds being broken are stronger than the bonds being made. ii) endothermic if the Cl-Br bond energy is greater than the bond energies for Cl-Cl and Br-Br.

3 Page 3 iii) exothermic if the Cl-Br bond energy is greater than the bond energies for Cl-Cl and Br-Br. iv) cannot say for certain without knowing the specific values for all bond energies. (e) Calculate the standard enthalpy change for the following equation: 2 NO 2 (g) 2 NO(g) + O 2 (g) i) +147 kj ii) -147 kj iii) +57 kj iv) 57 kj v) +114 kj vi) 114 kj (f) A piece of hot Zn is put into a beaker of cool ethanol and eventually the system reaches thermal equilibrium. Which of the following is NOT true of the process described? i) q Zn < 0 ii) T ethanol < 0 iii) energy flowed from Zn to ethanol iv) q zn = q ethanol Compound NO 2 (g) NO (g) H f at 298 K 33 kj/mol 90 kj/mol Free Response Questions-B (76 points in total) 4B. (10 pts) When sodium is added to excess water, it reacts with a bit of the water as indicated by the following thermochemical equation: 2 Na(s) + 2 H 2 O(l) 2 NaOH(aq) + H 2 (g) H = 368 kj How many grams of Na(s) must be added to 55.0 g of water to raise the temperature of the water from 24.1 ºC to 31.3 ºC? Assume standard conditions, a perfectly insulated cup, and negligible energy to heat the products. NOTE: The Na reacts with only a small fraction of the water in the cup, so also assume that there is still 55.0 g of water left after the reaction!

4 Page 4 6B. (8 pts) (a) Calculate H for the reaction represented by the following equation (assume all values are for 298 K): 2 CH 4 (g) + 4 Cl 2 (g) 2 CH 2 Cl 2 (g) + 4 HCl(g); H =??? given the following data: CH 2 Cl 2 (g) + HCl(g) CH 3 Cl(g) + Cl 2 (g); CH 4 (g) + Cl 2 (g) CH 3 Cl (g) + HCl(g) H = +104 kj H = kj Additional Problem (not actually given on a past exam): 10B. (8 pts) Your 238 ml cup of coffee was left too long in the microwave and is too hot to consume (assume it s 65 C). You drop in an ice cube (mass 9.2 g) to cool it down. The enthalpy of fusion (melting) for ice is 333 J/g. (a) How much energy will be needed to melt the ice cube? (b) Assuming the coffee has the properties of 238 g of water, what will be the temperature of the coffee after the ice cube has melted and everything in the cup is in thermal equilibrium? Assume no energy is given off to the air or to the cup. Note: To do this problem completely correctly is a bit tricky, but it is not nearly as hard to get it partially correct (i.e., to set up the problem incorrectly but solve what you set up correctly). During an exam it is better to do a problem partly correctly and possibly receive partial credit than to not do it at all.)

5 Page 5 13B. What is the standard enthalpy of formation of N 2 (g) and why? 13B (added) For each of the following substances, predict whether its standard enthalpy of formation is positive, negative, zero, or state that there not enough information to tell, and provide your reasoning. (a) NO(g) (b) Cl(g) (c) Fe(s) (d) H 2 (l) (e) Mg(NO 3 ) 2 (s) Section C-Quantum Mechanical Model of the Atom (up through electron configurations) 1C. Circle the correct answer (12 pts total) (2 points each) (a) The number of unpaired electrons in the ground state of an atom of phosphorus (P) is: (i) zero (ii) one (iii) two (iv) three (v) four (vi) five (vii) six (d) If the greenish line in the H-atom emission spectrum is due to a transition from the n = 4 energy level to the n = 2 energy level, and the red line is due to a transition from the n = x level to the n = 2 level, then x could be equal to: i) 1 ii) 2 iii) 3 iv) 4 v) 5 vi) any of the above 2C. Write T (True) or F (False) for the following statements. If the statement is false correct it by changing, dropping, or adding a few words (6 points) a) Mg 2+ is the common ion formed by Mg because the third ionization energy of Mg is extremely large. THIS QUESTION IS NOT ON EXAM 3B IT IS A PS10 KIND OF QUESTION (WHICH WILL BE COVERED ON EXAM 4) b) An atom having no unpaired electrons is paramagnetic. c) If electrons in a metal are ejected in a photoelectric effect using yellow light, then electrons will be ejected if blue light is used.

6 Page 6 Free Response Questions-C 5C. (6 pts) Calculate the wavelength, in nm, of the light that is just energetic enough to break apart Br 2 molecules into free atoms. The Br-Br bond energy is 193 kj/mol (of bonds). 7C. (5 pts) (a) Write the complete ground state electron configuration for Ru. 8C. (a) Write the orbital diagrams for (the ground state of [unless indicated otherwise]): (i) O (ii) O 2- (iii) Mg (iv) Mg 2+ (v) Any excited state of O (b) Which atom has a (ground state) electron configuration identical to that of Mg 2+? 9C. (2 pts) Light having which characteristic is most likely to be able to eject electrons from a metal? (a) small wavelength (b) low frequency (c) large amplitude (d) large photon density 11C. (5 pts) Calculate the wavelength of light corresponding to the n = 5 to n = 3 transition in the H atom.