Calculators are permitted. Computers, PDAs, and other electronic devices with a keyboard are not. Cell phones may not be used as calculators.

Transcription

1 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten his test is closed note/book One 8.5 x handwritten crib sheet (one sided) is ermitted. Please turn off your cell hone. Use a # encil. Calculators are ermitted. Comuters, PDAs, and other electronic devices with a keyboard are not. Cell hones may not be used as calculators. Comlete the Scantron card as shown below. Identify your version as indicated. Scantron errors are unishable by oint deductions. A total of 50 minutes will be allotted for the exam. Answer every question. here is no enalty for guessing. Circle Your Section Mindi Ogden A W 3-6 Denise Enekwa A W 3-6 Deborah Ortiz A3 W 3-6 Yo-Yuan Cheng A4 W 3-6 Wei Long A4 W 3-6 Chiaolong Hsiao B h 3-6 Michael Rood B h 3-6

2 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten. he heat gained by the system from the surroundings in a rocess carried out at constant ressure is a. w b. H c. - H d. E e. S Answer: b. Which one of the following statements is NO true concerning the equation below? N + 3H NH 3 H r = -460 kj a. he comlete reaction of.0 mole of H consumes 53 kj of heat. b. he comlete reaction of.0 mole of N roduces 460 kj of heat. c. he roduction of.0 mole of ammonia is accomanied by the roduction of 30 kj of heat. d. he comlete reaction of.38 mole of hydrogen requires 0.46 mole of nitrogen. e. All of these are true statements., the forward reaction roduces heat 3. he First Law of hermodynamics states that a. work and heat are interconvertable b. energy is conserved c. energy cannot be created or destroyed d. all of the above (a-c) e. none of the above Answer: d 4. Which of the following is not a state function? a. q b. E c. H d. G e. All of these are state functions. 5. Which of the following rocesses has H > 0? a. combustion of a hydrocarbon (gives off heat, H combust < 0) b. dilution of concentrated hydrochloric acid with water (gives off heat, H < 0) c. vaorization of water (absorbs heat, makes you, the surroundings, cold H > 0) d. freezing of liquid N (gives off heat, H < 0) e. all have H > 0

3 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten Answer: c 6. Calculate the [H + ] in a solution that is 0.0 M in NaF and 0.0 M in HF ( a = 7. x 0 4 ). a) 0.0 x 0 - M b) 7.0 x 0 4 M c).4 x 0 3 M d) 3.6 x 0 4 M e) none of these Answer: c [HF] [F - ] [H + ] I x0 - x C -x x x E (x0 - )-x ( x 0 - )+x 0-7 +x Assume 0 - >>x>>0-7 a = [H + ][F - ] = (0 - )(x)/(x0 - ) x=7. x 0-4 (x0 - )(0 + ) =.4x What quantity of NaOH(s) must be added to.00 L of 0.00 M HCl to achieve a H of.0? (assume constant volume.) a) 0.0 mole b) 0.4 mole c) 0. mole d) 0.0 mole e) none of these Answer: c 0. moles are required to bring the H to 7 (neutralize the HCl). 0.0 moles are required to bring the H from 7 to. 8. Consider the solution buffered by the weak acid HA. HA(aq) H + (aq) + A - (aq) Which of the statements below is false? a) Addition of NaCl(s) to roduce Na + (aq) and Cl - (aq) will change the H. False: NaCl is not an acid or base, and there is no common ion. b) If the ratio of [A - ]/[HA] is constant, the H is constant. rue: H=a+log[A - ]/[HA] c) he solution resists change in H when acid or base is added. rue: that is the definition of a buffer. d) he buffering caacity is maximum when H= a. rue: H=a+log[A - ]/[HA] and the % change of [A - ]/[HA] with change in [A - ] is a minimum when [A - ]/[HA] =. e) H=a+log[A - ]/[HA]. rue: hat is the Henderson-Hasselbalch equation. 3

4 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten Given the following enthalies of formation: Secies H f (kj mol ) glucose [C 6 H O 6 (s)] 74 CO (g) 393 H O(l) What is the standard enthaly of combustion of glucose to form carbon dioxide and liquid water. a. 800 kj mol b. 953 kj mol c. 595 kj mol d. 595 kj mol e. none of these C 6 H O 6 (s) + 6O = 6H O(l) + 6CO (g) H f (O ) = 0 H r = 6(-86)+6(-393)-(-74) = = -800 kj mol A erfect gas is very slowly comressed from 45 L to 8 L at a constant external ressure of 5.0 atm. During this rocess 9.8 kj of energy is released as heat. 0. he heat q for this rocess is a. 35 kj b. 35 kj c. 9.8 kj d. 9.8 kj e. 70 kj Answer: c, if q is released to the surroundings, q sys <0.. he work w for this rocess is a. 9.8 L atm b. 9.8 L atm c. 35 L atm d. 35 L atm e. 70 kj Answer: c w=-pδv = -5(8-45)=35 L atm. In any rocess, E univ = a. 0 b. E sys c. E surr d. E sys e. E surr 4

5 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten 3. Given the following H f values: SiH 4 (g) 34.3 kj mol SiO (s) 90.9 kj mol H O(l) 85.8 kj mol O (g) 0.0 kj mol Also, H O H va = 44.0 kj mol. Calculate H r for SiH 4 (g) + O (g) SiO (s) + H O(s). a. 57 kj mol b. 49 kj mol c. 87 kj mol d. his cannot be determined without additional information. e. none of these Answer: d, you need to know H fusion for H O. 4. he second law of thermodynamics states that a. energy is conserved in sontaneous rocesses. b. the heat content of the universe increases during a sontaneous rocess. c. the entroy of the universe increases during a sontaneous rocess. d. the entroy of a erfect crystal is zero at absolute zero. e. work and heat are interconvertable. Answer: c 5. For the vaorization of a liquid at its boiling oint b, the change in entroy and the change in enthaly are related by a. S va = H va / b b. S va = b H va c. S va = b / H va d b = H va S va e. here is no general relation covering these vaorization quantities., at the boiling oint 0=ΔG=ΔH va - b ΔS va 6. If S univ is ositive for a rocess, the rocess is, if S univ for a rocess is negative, the rocess is, and if the S univ for a rocess is zero, the rocess is. a. at equilibrium, sontaneous, nonsontaneous b. nonsontaneous, sontaneous, at equilibrium c. sontaneous, at equilibrium, nonsontaneous d. sontaneous, nonsontaneous, at equilibrium e. none of these Answer: d 5

6 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten 7. A rocess can roceed sontaneously in the forward direction at low temeratures and in the reverse direction at high temeratures if a. H is ositive and S is negative. b. H is negative and S is ositive. c. both H and S are ositive. d. both H and S are negative. e. his cannot be answered in such a general way. Answer: d: ΔG=ΔH-ΔS. At low the ΔH term dominations and ΔH < 0 will drive reaction forward. At high, ΔS term dominates and ΔS < 0 will drive the reaction in reverse. 8. Methyl orange is an indicator with a a of 0-4. he rotonated form of methyl orange is red, while the derotonated form is yellow. At H 6.0, the indicator will be a) red. b) orange. c) yellow. d) blue. e) not enough information Answer: c: When the H > a, the redominant secies is derotonated. ( a = 4) 6

7 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten 9. I have followed the instructions on the first age. I have entered my G number, my name, the exam version, and my section number. a. rue b. False 0. his is exam version: a. A b. B c. C Answer: A,B,C 7

8 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten Constants: mole = 6.0 x 0 mole = 6.0 x 0 mole = 6.0 x 0 h = 6.66x0 Js m J (Joule) = kg s 8 c = 3.0x0 m / s atoms molecules ions Mass of an Electron = x 0 Mass of a Proton =.67 x 0 Mass of a Neutron =.67 x 0 Latm R = 0.08 mol J R = 8.3 mol V. P.( H O,373) = 760torr kg kg -3 kg Stoichiometry: mass Density = volume mole of solute Molarity = M = L of solvent mass n (number of moles) = Molar Mass M V = M V Quantum Mechanics c = &' E = mc & = # h H% = E% h " x* m" v 4$ Maximum Occuancy = n Solubility Rules. All alkali metal salts are soluble.. All ammonium (NH4 + ) salts are soluble. 3. All chlorides, bromides, and iodides are soluble excet those of Ag +, Hg +, and Pb All nitrates, chlorates, and erchlorates are soluble. 5. All sulfates excet those of Ca +, Sr +, Ba +, Pb +, Hg +, and Ag All carbonates, chromates, oxalates, and hoshates are insoluble excet those of the alkali metals and ammonium. 7. All hydroxides are insoluble excet those of the alkali metals. Bonding Formal Charge = V (L S) V = Number of Valence Electrons L = he Number of Lone Pair Electrons S = he Number of Shared Electrons 8

9 Chem. 30 Sring 008 Exam 3 VERSION A Professors Williams/Whetten Solutions o P = X P mol of solute m = molality = kg of solvent " " X f b = # m = m = MR Gas Laws PV b n = mole fraction = n V f E (article) = PV = nr PV total o elvin= C n ( P + a )( V nb) = nr V P = P + P P total = P = V PV = 3 E( mol) = R (monoatomic) mu n Acid-Base H = log OH = log HA( aq) " H B( aq) " BH w = a = log w = 4 at 5 + [ H ] [ OH ] H + OH = 4 a w b a b + [ H ][ A ] = [ HA] = # [ BH ][ OH = [ B] ( aq) + A ( aq) at 5 + ( aq) + OH a o C o ] C & [ base] # H = a + log$ %[ acid ]" ( aq) hermodynamics E = q + w w = ' P ( V 5 C = R (monoatomic ideal gas) 3 Cv = R (monoatomic ideal gas) ( H = q (constant temerature) w rev ext & V = ' nr ln $ % V # " q = mc q q dq ds = G = H " S G = " R ln c C v = nc = nc H = S water V = 4.84 J mol 9