CHEM 1312 Exam 3

For the combustion of acetylene at 298.15 K, 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g) calculate ΔS°(universe) given ΔS°(system) = -194.6 J/K and ΔH°(system) = -2511.2 kJ. -2453.2 J/K -186.2 J/K +186.2 J/K +1290.4 J/K +8228.0 J/K

+8228.0 J/K ΔS uni = ΔS sys + ΔS surr ΔS surr = ΔH/T = 2.5E6/298.15 = 8.4E3 ΔS uni = -194.6+8.4E3

Determine Eo for the following reaction, using the given standard reduction potentials: Cr3+(aq) + Sn(s) → Cr2+(aq) + Sn2+(aq) Eo for Sn2+(aq) = -0.14 V Eo for Cr3+(aq) = -0.41 V

-0.27 Eo = -.41 + .14

Consider the reaction between sulfite and a metal anion, X2-, to form the metal, X, and thiosulfate: 2 X2-(aq) + 2 SO32- + 3 H2O(l) → 2 X(s) + S2O32- (aq) + 6 OH- for which Eo cell = 0.17. Given that the Eo red for sulfite is -0.57 V, what is the value of Eo red for X?

-0.74 SO32- is reduced X2- is oxidized -0.57-x = 0.17

At a certain temperature, 389, Kp for the reaction, H2(g) + Br2(g) ⇌ 2 HBr(g) is 8.83 x 10^21. Calculate the value of ΔGo in kJ for the reaction at 389 K.

-1.63E2 ΔG=-RTlnK

What is the value of ΔGo in kJ at 25 oC for the reaction between the pair: Sn(s) and Pb2+(aq) to give Pb(s) and Sn2+(aq)? Sn2+(aq)+2e− → Sn(s) -0.14 Pb2+(aq)+2e− → Pb(s) -0.13

-1.93 Pb2+ + Sn→ Pb + Sn2+ Eo cell = -.13 + .14 = .01 ΔG = -nFEo ΔG = -2 * 96485 * .01 ΔG = -1.93 KJ

Given the values of ΔGfo given below in kJ/mol calculate the value of ΔGo in kJ for the reaction, NH3(g) + HBr(g) → NH4Br(s) ΔGfo (NH3(g)) = -22. ΔGfo (HBr(g)) = -52. ΔGfo (NH4Br(s)) = -179.

-105 -179-(-22+-52)

A particular reaction has a ΔHo value of -174. kJ and ΔSo of -137. J/mol K at 298 K.Calculate ΔGo at 321. K in kJ, assuming that ΔHo and ΔSo do not significantly change with temperature.

-130 ΔG = ΔH - TΔS ΔG = -174000 - 321(-137) = -1.3E5 = -130 kJ

Calculate the standard entropy change for the following reaction, 2 SO2(g) + O2(g) → 2 SO3(g) given S°[SO2(g)] = 248.2 J/K⋅mol, S°[O2(g)] = 205.1 J/K⋅mol, and S°[SO3(g)] = 256.8 J/K⋅mol -196.5 J/K -94.0 J/K -187.9 J/K +187.9 J/K +196.5 J/K

-187.9 J/K

The value of ΔGo for the reaction, N2(g) + 3 H2(g) ⇌ 2 NH3(g) is -32.90 kJ at 298 K. Calculate the value of ΔG in kJ at 298 K if the partial pressures of N2, H2 and NH3 are 1.64, 4.95, and 75.2 atm respectively.

-24.6 Find Q and use ΔG = ΔGo + RTlnQ -3.29E4+8.31(298)ln(28.4)

At 417 K., ΔGo equals 122 kJ for the reaction, Cl2(g) ⇌ 2 Cl(g) Calculate the value of ln(K) for the reaction at this temperature.

-3.52E1 ΔG=-RTlnK 122000 = -8.31(417)lnK lnK = -35.2

The value of ΔGo for the precipitation reaction, Ca2+(aq) + CO32-(aq) ⇌ CaCO3(s) is −48.1 kJ at 298 K. Calculate the value of ΔG in kJ at 298 K if the concentrations are [Ca2+] = 0.604 M and[CO32−] = 0.663 M.

-45.8 Q= 1/(0.663*0.604) convert to KJ

Given the following data: 2 Fe(s) + 3/2 O2(g) ⇌ Fe2O3(s) , ΔGo = -746. CO(g) + ½ O2 ⇌ CO2(g), ΔGo = -251. Find ΔGo for Fe2O3(s) + 3 CO(g) ⇌ 2 Fe(s) + 3 CO2(g).

-7 746-3(251)

Calculate the value of ΔGo in kJ for the combustion of 1 mole of methane to form carbon dioxide and gaseous water at 298 K.(value ± 2) So given below in J/mol K S° (CH4(g)) = 187. S° (O2(g)) = 204. S° (CO2(g)) = 219. S° (H2O(g)) = 183. ΔHfo given in kJ/mol ΔHfo (CH4(g)) = -75. ΔHfo (CO2(g)) = -399. ΔHfo (H2O(g)) = -235.

-791 CH4 + 2O2 → CO2 + 2H2O ΔHfo = (2(-235) -399) - (-75) = -794 S°= (2(183)+219)) - (187+2(204)) = -10 = -.01 ΔG = ΔH - TΔS ΔG = -794 - 298(-.01) = -791

Calculate Eo cell for the reaction: Ag+(aq) + MnO2(s) → MnO4-(aq) + Ag(s) (in basic solution) The reduction potential for Ag+(aq) is +0.80 V and for MnO4-(aq) is +0.60 V.

.2 Eo = .8 - .6

A voltaic cell consists of an Zn/Zn2+ half-cell and a Cd/Cd2+ half-cell. The standard reduction potential for Zn2+ is −0.76V and for Cd2+ is −0.40 V. Calculate Ecell at 25 ºC when the concentration of [Cd2+] = 9.05 x 10-6 M and [Zn2+]= 3.76 x 10-4 M.

.31 Zn2+ oxidized Cd2+ reduced Zn + Cd2+ -> Zn2+ + Cd Eo cell = -.4+.76 = .36 Ecell = .36 - .0591/2 log (3.76 x 10-4/9.05 x 10-6) = .31

A voltaic cell consists of an Al/Al3+ half-cell and a Ag/Ag+ half-cell. Calculate [Ag+] when [Al3+] = 0.603 M and Ecell = 2.46 V. Use reduction potential values of Al3+ = −1.66 V and for Ag+ = +0.80 V.

.845 Eo cell = .8+1.66 = 2.46 3Ag+ + Al -> Al3+ + Ag E = Eo - .0591/n log Q 2.46 = 2.46 - .0591/3 log ( .603/x^3)

A beta particle is

0,-1 e

Which one of the following is a correct representation of a positron?

0,1 e

Calculate Eocell for the reaction: Co(s) + H+(aq) → Co2+(aq) + H2(g). The reduction potential for Co2+(aq) is -0.28 V.

0.28 0+.28 = .28

How many grams of aluminum may be formed by the passage of 4,064 C through an electrolytic cell that contains a molten aluminum salt.

0.379 Al3+ + 3e- ------> Al 3 e * 96485 C/1 e = 289455 C Q = 4,064 C mol of Al plated = 4,064/289455 = .014 mol mass Al = .014 mol * 26.98g/mol = 0.379

An atom of 108In has a mass of 107.909678 amu. mass of1H atom = 1.007825 amu mass of a neutron = 1.008665 amu Calculate the mass defect (deficit) in amu/atom.

0.985 # neutrons: 108-49 = 59 m defect= (49*1.007825 + 59*1.008665)- 107.909678 = .985 amu

The equilibrium constant for the reaction, 2 Fe3+(aq) + Hg22+(aq) ⇌ 2 Fe2+(aq) + 2 Hg2+(aq) is Kc = 9.1 x 10-6 at 298 K. Calculate ΔG in J with the concentration values given below. [Fe3+] = 0.363 M [Hg22+] = 0.0583 M [Fe2+] = 0.0343 M [Hg2+] = 0.0644 M.

10,518.8 ΔGo= RTlnK ΔGo = -8.31(298)ln(9.1 x 10-6) ΔGo = 28757.76 J ΔG = ΔGo + RTlnQ Q = (0.0343^2) (0.0644^2) / (0.363^2) (0.0583) = 6.4E-4 ΔG = 28757.76+ 8.31(298)ln6.4E-4 = 10,518.8

How many amps are required to produce 23.6 g of iron metal from a solution of aqueous iron(III)chloride in 2.87 hours?

11.8 m=ZIt convert hrs to sec

Write a balanced reaction for the decay of barium-127 by positron emission.

127,56 Ba -> 0,+1Ba + 127, 55 Ba

If astatine-207 decays by α emission, followed by α emission, followed by electron capture, what nucleus is produced?

199, 80 Pb 207-4-4-0 = 199 85-2-2-1 = 80

Consider the following half-reactions. Au+(aq) + e- → Au(s), Eo = 1.69 V N2O(g) + 2 H+(aq) + 2 e- → N2(g) + H2O(l), Eo = 1.77 V Cr3+(aq) + 3 e- → Cr(s), Eo = -0.74 V What is the maximum value of Eo of a cell constructed using two of these half-equations?

2.51 Reduction (largest Eo) N2O(g) + 2 H+(aq) + 2 e- → N2(g) + H2O(l) Oxidation (smallest Eo) (flip) Cr(s) → Cr3+(aq) + 3 e- Eo = +0.74 V 0.74 + 1.77 = 2.51 V

How many grams of cobalt may be formed by the passage of 2.2 amps for 1.75 hours through an electrolytic cell that contains an aqueous cobaltic (Co(III)) salt.

2.82 Co3+ + 3e- ==> Co(s) 2.2 C/s * 60s/min * 60min/hr * 1.75 hr = 13860C 13860C * 1e/96485C *1mol/3e = .048 mol .048mol* 58.93 g = 2.82

Iron-59 is a radioactive nuclide (t1/2 = 46 d) used in anemia diagnosis. If the initial count rate of an 59Fe sample is 560 counts/min., how long will it take (days) for the count to drop to 400 counts/min.? Enter your answer with one decimal place and no units.

22.3 t = 1/k ln No/N t = t half/.693 ln No/N t = 46/.693 ln 560/400

What nucleus, if it decays by successive beta, beta and alpha emissions, would produce uranium-236?

240, 92 U X -> U + 2e +He mass X = mass U + mass e + mass He M = 1(236) + 2(0) + 1*4 M = 240 atomic X = atomic U + atomic e + atomic He A = 1(92) + 2(-1) + 1*2 A = 92

The mass defect for the formation of lithium-6 is 0.0343 g/mol. The binding energy for lithium-6 nuclei is ________ kJ/mol. Enter your answer in exponential format (sample 1.23E-4) with two decimal places and no units.

3.09E9 0.0343 g/mol /1000 = .0343E-3 kg/mol E=mc^2 .0343E-3 (3x10^8)^2 = 3.09E12 J/mol = 3.09E9 kJ/mol

Which one of the following is a correct representation of an alpha particle?

4,2 He

What is the value of the equilibrium constant, K, at 25 oC for the reaction between the pair: Br2(l) and I−(aq) ? Br2(l)+2e− → 2Br−(aq) +1.09 I2(l) + 2e− → 2I−(aq) +0.54

4.02E18 Br2(l) + 2I-(aq) -----> I2(l) + 2 Br-(aq) Eo cell = 1.09- .54 =.55 log K = nEo/.0591 log K = 2(.55) / .0591

How long (in hours) must a current of 2.05 amps be passed to produce 60.5 g of iron metal from a solution of aqueous iron(III)chloride?

42.53 m = ZIt Z = E/F I = 2.05 m = 60.5 F = 96485 E = 55.8g/3 e- = 18.6 60.5 = 18.6/96485 * 2.05 * t t = 153091s/3600s = 42.53 hr

An atom of 75Ga has a mass of 74.926500 amu. mass of1H atom = 1.007825 amu mass of a neutron = 1.008665 amu Calculate the binding energy in kilojoule per mole.

6.27E10 # neutrons: 75-31 = 44 m defect= (31*1.007825 + 44*1.008665)- 74.926500 = .697 .697*1.66× 10⁻²⁷ kg = 1.16E-27 E = 1.16E-27(2.99792x10E8)^2 = 1.04E-10 J = 1.04E-13 kJ/atom 1.04E-13 * (6.023 × 10²³) = 6.27E10 kJ/mol

A particular reaction has a ΔHo value of -186. kJ and ΔSo of -307. J/mol K at 298 K. Assuming that ΔHo and ΔSo do not significantly change with temperature, determine the temperature in K at which the spontaneity of this reaction changes.

606 ΔG = ΔH - TΔS 0 = ΔH - TΔS for spontaneity 0 = -186 + T(.307) T = 606

A particular reaction has a ΔHo value of -140. kJ and ΔGo of -154. kJ at 221. K.Calculate ΔSo at 221. K in J/K.

63.3 -154 = -140 - 221ΔS

An atom of 90Br has a mass of 89.930638 amu. mass of1H atom = 1.007825 amu mass of a neutron = 1.008665 amu Calculate the binding energy in MeV per atom.

764 # neutrons: 90-35 = 55 m defect= (35*1.007825 + 55*1.008665)- 89.930638 = .82 amu E = .82 (931.5) = 764 MeV/atom

An atom of 90Kr has a mass of 89.919517 amu. mass of1H atom = 1.007825 amu mass of a neutron = 1.008665 amu Calculate the binding energy in MeV per nucleon.

8.59 # neutrons: 90-36 = 54 m defect= (36*1.007825 + 54*1.008665)- 89.919517 =.83 amu E = .83 (931.5) = 773 MeV/atom 773/90 nucleons = 8.59 MeV per nucleon

What isotope (?) is needed to balance the nuclear fission reaction below? 1,0 n + 235,92 U → 137,52 Te+ ? + 2 1,0 n

97, 40 Zr 235-137-1 = 97 92-52 = 40

Balance the following equation in acidic solution using the lowest possible integers and give the coefficient of H+. Cl2(aq) + S2O32- (aq) → Cl-(aq) + SO42-(aq) A. 10 B. 3 C. 2 D. 8 E. 1

A. 10 O: S2O32- → 2SO42- R: Cl2 → 2Cl- O: S2O32- + 5H2O → 2SO42- + 10H+ + 8e- R: (Cl2 + 2e- → 2Cl-) 4

Balance the following equation in acidic solution using the lowest possible integers and give the coefficient of water. ClO3-(aq) + Br-(aq) → Br2(l) + Cl-(aq) A. 3 B. 2 C. 6 D. 1

A. 3 O: 2Br- → Br2 R: ClO3- → Cl- O: (2Br- → Br2 + 2e-) 3 R: ClO3- → Cl- + 3H2O ClO3- + 6H+ → Cl- + 3H2O ClO3- + 6H+ + 6e- → Cl- + 3H2O

Balance the following equation in basic solution using the lowest possible integers and give the coefficient of water. PbO(s) + NH3(aq) → N2(g) + Pb(s) A. 3 B. 2 C. 6 D. 1

A. 3 O: 2NH3 → N2 R: PbO → Pb O: 2NH3 → N2 + 6H+ 2NH3 + 6OH- → N2 + 6H2O 2NH3 + 6OH- → N2 + 6H2O + 6e- R: PbO → Pb + H2O PbO + 2H+ → Pb + H2O PbO + 2H2O → Pb + H2O + 2OH- (PbO + 2H2O + 2e- → Pb + H2O + 2OH-) 3

When an aqueous solution of NaBr is electrolyzed, what forms at the electrodes? A. Cathode: H2; anode: Br2 B. Cathode: H2; anode: O2 C. Cathode: Br2; anode: Na D. Cathode: Br2; anode: H2 E. Cathode: Na; anode: Br2

A. Cathode: H2; anode: Br2

The rad is a measure of the A. amount of radiation absorbed by tissue where 1 rad corresponds to 0.01 J of energy absorbed by 1 kilogram of tissue. B. total energy absorbed by an object exposed to a radioactive source. C. lethal threshold for radiation exposure. D. number of alpha particles emitted by exactly one gram of a radioactive substance. E. none of these is correct.

A. amount of radiation absorbed by tissue where 1 rad corresponds to 0.01 J of energy absorbed by 1 kilogram of tissue.

U-238 reacts with what particle to make 3 neutrons and 239Pu? A. an alpha particle B. a neutron C. a proton D. a beta particle E. a positron

A. an alpha particle 239Pu has 94 protons and 239- 94 = 145 neutrons. 238U has 92 protons and 238 - 92 = 146 neutrons

Which of the following elements can be isolated by electrolysis of the aqueous salt shown? A. oxygen from AgNO3(aq) B. phosphorus from Na3PO4(aq) C. sulfur from CuSO4(aq) D. oxygen from FeCl3(aq) E. potassium from KCl(aq)

A. oxygen from AgNO3(aq)

When the nuclides which do not undergo radioactive decay are plotted on a neutron/proton grid they make up a group called A. the "zone of stability." B. the "peninsula of nuclear stability." C. the "sea of instability." D. the "island of instability." E. the "zone of instability.

A. the "zone of stability."

For the reaction, Fe2O3 (s) + 3 H2(g) <=> 2 Fe(s) + 3 H2O(g), ΔG° = 53 kJ at 25 °C and ΔH° = 100 kJ. Which of the following is completely true about the relationship between ΔG and T for this reaction? A. ΔG < 0 when T > 635 K B. ΔG > 0 when T > 635 K C. ΔG < 0 when T > 0.6 K D. ΔG < 0 when T < 630 K E. ΔG < 0 when T < 0.6 K

A. ΔG < 0 when T > 635 K 53 = 100 -298ΔS ΔS = .16

When 222,86 Rn decays in a 5-step series the product is 210,82 Pb. How many alpha and beta particles are emitted in the decay series? A. 2 alpha, 3 beta B. 3 alpha, 2 beta C. 4 alpha, 1 beta D. 1 alpha, 4 beta E. either 2 alpha, 3 beta or 1 alpha, 4 beta

B. 3 alpha, 2 beta 222-4-4-4 =210 86-2-2-2+1+1 = 82

What product(s) forms at the anode in the electrolysis of an aqueous solution of FeBr2? A. H2 and OH- B. Bromine C. Fe D. O2 and H+

B. Bromine

Hydrogen can be prepared by suitable electrolysis of aqueous cupric (Cu(II)) salts A. True B. False

B. False Electrolysis of water gives pure hydrogen at anode

In the electrolysis of molten MgCl2, which product forms at the cathode? A. H2(g) B. Mg(l) C. O2(g) D. Cl2(g)

B. Mg(l) Mg2+ + 2e- ==> Mg(s)

Consider the following half-reactions and their standard reduction potentials then give the standard line (cell) notation for a voltaic cell built on these half reactions. Mn2+(aq) + 2 e- <=> Mn(s) E° = -1.18 V Fe3+(aq) + 3 e- <=> Fe(s) E° = -0.036 V A. Mn (s) | Mn 2+(aq, 1.0 M) || Fe(s) | Fe3+(aq, 1.0 M) B. Mn (s) | Mn 2+(aq, 1.0 M) || Fe3+(aq, 1.0 M) | Fe(s) C. Fe(s) | Fe3+(aq, 1.0 M) || Mn (s) | Mn 2+(aq, 1.0 M) D. Fe(s) | Fe3+(aq, 1.0 M) || Mn2+(aq, 1.0 M) | Mn(s)

B. Mn (s) | Mn 2+(aq, 1.0 M) || Fe3+(aq, 1.0 M) | Fe(s)

What product(s) forms at the anode in the electrolysis of an aqueous solution of K3PO4? A. Phosphorus B. O2 and H+ C. K D. H2 and OH-

B. O2 and H+ Neither K⁺ nor PO₄³⁻ can oxidize because K and P are in their highest oxidation states. Then, oxygen in water will oxidize according to the following half-reaction: Oxidation: 2 H₂O(l) → O₂(g) + 4 H⁺(aq) + 4 e⁻

Silicon-29 can be made when a nucleus is bombarded with very strong electromagnetic radiation. If a proton and a neutron are also formed, what is the reactant nucleus? A. Phosphorus-30 B. Phosphorus-31 C. Aluminum-31 D. Aluminum-27

B. Phosphorus-31 29, 14 Si + 1P1 + 0n1 sum of protons/e = 14+1+0 = 15 sum of mass # = 29+1+1 = 31 reactant nucleus contains is 15P31

121Sb is expected to be stable. A. False B. True

B. True

Cobalt metal can be prepared by electrolysis of its aqueous salts A. False B. True

B. True only calcium cannot be

"Which nuclear decay process decreases the neutron/proton ratio? A. alpha emission B. beta emission C.electron capture D. positron emission E. none of these

B. beta emission

A radioisotope has a neutron/proton ratio which is too low. Which of the following processes is least likely to occur for such a nucleus? A. alpha emission B. beta emission C. electron capture D. positron emission E. all the above are equally likely to occur

B. beta emission

Which of the following statement(s) is/are correct? i) The energy change when 16,8 O is (hypothetically) formed from 8 protons and 8 neutrons is known as the energy defect. ii) The splitting of a heavier nucleus into two nuclei with smaller mass numbers is known as nuclear fission. iii) The first example of nuclear fission involved bombarding U with He nuclei. A. i) only B. ii) only C. iii) only D. i) and ii) only E. i) and iii) only F. ii) and iii) only G. i), ii) and iii) H. None of the choices are correct.

B. ii) only

If a nucleus emits an alpha particle A. its atomic number decreases by four and its mass number decreases by two. B. its atomic number decreases by two and its mass number decreases by four C. its atomic number increases by two and its mass number decreases by two. D. its atomic number is unchanged and its mass number is unchanged. E. its atomic number is unchanged and its mass number decreases by four.

B. its atomic number decreases by two and its mass number decreases by four

Balance the following equation in basic solution: NO2(g) → NO2-(aq) + NO3-(aq) What is the coefficient of water? A. 2 B. 8 C. 1 D. 6 E. 4

C. 1 O: NO2 → NO3- NO2 + H2O → NO3- NO2 + H2O → NO3- + 2H+ NO2 + H2O + 2OH- → NO3- + 2H2O NO2 + H2O + 2OH- → NO3- + 2H2O + e- R: NO2 → NO2- NO2 + e- → NO2-

The number of disintegrations per minute (dsm) of a sample of iodine-133 is measured at 5.5 × 102 dsm. When the sample is measured 295 minutes later, the number of disintegrations has decreased to 4.7 × 102 dsm. What is the half-life of iodine-133? A. 5.7 × 10-4 m. B. 2.6 m. C. 1.3 × 103 m. D. 3.9 × 102 m. E. 9.7 × 104 m.

C. 1.3 × 103 m ln(N/No) =-kt ln(4.7 × 102/5.5 × 102) = -k295 k = 5.3E-4 t1/2 = .693/5.3E-4 = 1.3E3

The number of nucleons in a 236, 92 U 2+ nucleus is A. 92 B. 144 C. 236 D. 328 E. None of these

C. 236 mass # = nucleons #

If we start with 1.000 g of strontium-90, 0.908 g will remain after 4.00 yr. This means that the of strontium-90 is __________ yr. A. 3.05 B. 4.40 C. 28.8 D. 3.63 E. 41.6

C. 28.8 ln(N/No) = -kt ln(.908/1) = -k4 k = .024 k = .693/t half t = 28.8

The number of neutrons in 55,26 Fe 2+ is A. 26 B. 23 C. 29 D. 53 E. 55

C. 29 55-26

210Pb has a half-life of 22.3 years and decays to produce 206Hg. If you start with 7.50 g of 210Pb, how many grams of 206Hg will you have after 17.5 years? A. 4.35 B. 3.15 C. 3.09 D. 0.0600 E. 1.71

C. 3.09 k = .693/22.3 = .03 log(No/N) = kt ln(N/7.5) = .03(17.5) N = 4.4 7.5-4.4 = 3.15 3.15/210 * 206 = 3.09

Balance the following equation in basic solution using the lowest possible integers and give the coefficient of water. AlH4-(aq) + H2CO(s) → Al3+ (aq) + CH3OH(aq) A. 0 B. 2 C. 4 D. 3 E. 1

C. 4 O: AlH4- → H2O + Al3+ AlH4- + H2O → H2O + Al3+ AlH4- + H2O → H2O + Al3+ + 4H+ AlH4- + H2O + 4OH- → H2O + Al3+ + 4H2O AlH4- + H2O + 4OH- → H2O + Al3+ + 4H2O + 8e- R: H2CO → CH3OH H2CO + 2H+ → CH3OH H2CO + 2H2O → CH3OH + 2OH- (H2CO + 2H2O + 2e- → CH3OH + 2OH-) 4 When one member of the redox couple is oxygen with an oxidation state of -2 or hydrogen with an oxidation state of +1, it is best to replace it with a water molecule.

Which of the following elements would you expect to have the most stable nuclides? Element number: A. 47 B. 48 C. 50 D. 51 E. 52

C. 50 2, 8, 20, 50, 80 or 126 protons/neutrons are stable

In the electrolysis of molten CoCl2, which product forms at the cathode? A. Cl2(g) B. O2(g) C. Co(l) D. H2(g)

C. Co(l) Co2+ + 2e- ==> Co(s)

Using the standard reduction potentials, Pb2+(aq) + 2e- → Pb(s), E° = -0.13 V Fe2+(aq) + 2e- → Fe(s), E° = -0.44 V Zn2+(aq) + 2e- → Zn(s), E° = -0.76 V which metal will reduce Mn3+ to Mn2+ (E°red = +1.51 V) but will not reduce Cr3+ to Cr2+ (E°red = -0.40 V) A. Zn only B. Pb and Fe C. Pb only D. Pb, Fe, and Zn E. Fe and Zn

C. Pb only

For the gas phase reaction N2 + 3 H2 <=> 2 NH3 ΔHº = -92 kJ for the forward reaction. In order to decrease the yield of NH3, the reaction should be run A. at high P, low T. B. at high P, high T. C. at low P, high T. D. at high P, but is independent of T. E. at low P, low T.

C. at low P, high T. This is exothermic, favor low T. High T will favor reverse rxn forward rxn: 4mol -> 2mol Volume must increase to favor backward rxn. P is inv pro to V so increase V will decrcease P

Which one of the following devices converts radioactive emissions to light for detection? A. Geiger counter B. photographic film C. scintillation counter D. none of these E. radiotracer

C. scintillation counter

Balance the following equation in basic solution using the lowest possible integers and give the coefficient of water. P4(aq) → H2PO2-(aq) + PH3(g) A. 4 B. 0 C. 2 D. 3 E. 1

D. 3 O: P4 → 4H2PO2- R: P4 → 4PH3 O: P4 + 8H2O → 4H2PO2- P4 + 8H2O → 4H2PO2- + 8H+ P4 + 8H2O + 8OH- → 4H2PO2- + 8H2O (P4 + 8H2O + 8OH- → 4H2PO2- + 8H2O + 4e-) 3 R: P4 + 12H+ → 4PH3 P4 + 12H2O → 4PH3 + 12OH- P4 + 12H2O + 12e- → 4PH3 + 12OH-

The half-life of 223Ra is 11.4 days. How much of a 200.0 mg sample remains after 600 hours? A. 0.219 mg B. 21.9 mg C. .0302 mg D. 43.8 mg E. 6.04 mg

D. 43.8 mg k = .693/11.4 = .0608 t = 25 days N = Noe^-kt N = 200e^-.0608*25

Given that the ∆G°f (kJ/mol) at 298 K for difluoroacetylene (C2F2) and hexafluorobenzene (C6F6) are 185.3 and 81.3, respectively, what is K at 298 K for the reaction, C6F6(g) ⇌ 3C2F2(g)? A. 5.89 x 10-19 B. 1.70 x 1018 C. 1.21 D. 6.41 x 10-84 E. 0.826

D. 6.41 x 10-84 ∆G°f = 3(185.3)-81.3 = 474.6 = 4.7E5 J ∆G° = -RTlnK 4.7E5 J = -8.31(298)lnk

When a solution containing M(NO3)2 of an unknown metal M is electrolyzed, it takes 74.1 s for a current of 2.00 A to plate out 0.0737 g of the metal. The metal is A. Ti B. Cd C. Cu D. Mo E. Rh

D. Mo 2.00 C/s x 74.1 s x 1 mol e-/96485 C = 0.001536 mol e- 0.001536 mol e- / 2 = 0.000768 moles M 0.0737 g M/0.000768 mol M = 95.96 g

The exothermic reaction 2NO2(g) <=> N2O4(g), is spontaneous... A. need to know more information B. never C. at high temperatures D. at low temperatures E. at all temperatures

D. at low temperatures 2 mol of gas to 1 mol => ∆S neg ∆G = ∆H - T∆S a low temp make -∆G

Which of the following statement(s) is/are correct? i) Breeder reactors convert the non-fissionable nuclide, 238U to a fissionable product. ii) The most stable nucleus in terms of binding energy per nucleon is 56Fe. iii) Electric power is widely generated using nuclear fusion reactors. A. i) only B. ii) only C. iii) only D. i) and ii) only E. i) and iii) only F. ii) and iii) only G. i), ii) and iii) H. None of the choices are correct.

D. i) and ii) only

Which of the following statement(s) is/are correct? i) The mass defect is the difference in mass between that of a nucleus and the sum of the masses of its component nucleons. ii) The splitting of a heavier nucleus into two nuclei with smaller mass numbers is known as nuclear fission. iii) The first example of nuclear fission involved bombarding with nuclei. A. i) only B. ii) only C. iii) only D. i) and ii) only E. i) and iii) only F. ii) and iii) only G. i), ii) and iii) H. None of the choices are correct.

D. i) and ii) only

Balance the following equation in acidic solution using the lowest possible integers and give the coefficient of water. Sb(s) + NO3-(aq) → Sb4O6(s) + NO(g) A. 3 B. 5 C. 4 D. 6 E. 2

E. 2 O: 4Sb → Sb4O6 R: NO3- → NO O: 4Sb + 6H2O → Sb4O6 4Sb + 6H2O → Sb4O6 + 12H+ 4Sb + 6H2O → Sb4O6 + 12H+ + 12e- R: NO3- → NO + 2H2O NO3- + 4H+ → NO + 2H2O (NO3- + 4H+ + 3e- → NO + 2H2O) 4

A freshly prepared sample of curium-243 undergoes 3312 disintegrations per second. After 6.00 yr, the activity of the sample declines to 2755 disintegrations per second.The half-life of curium-243 is ________ yr. A. 4.99 B. 32.6 C. 7.21 D. 0.765 E. 22.6

E. 22.6 ln(2755/3312) = -k6 k = .031 t= .693/0.0301= 22.6

241, 95 Am is used in many home smoke alarms. If 85% of the americium in a smoke detector decays in 1250 years, what is the half-life of this isotope? A. 1.52 x 10-3 yr B. 7.35 x 102 yr C. 5.33 x 103 yr D. 5.78 x 103 yr E. 4.57 x 102 yr

E. 4.57 x 102 yr 241*.15 = 36.15 left ln(36.15/241) = -k1250 k = 1.5E-3 t 1/2 = .693/1.5E-3 = 4.57 x 102

Which of the following reactions will have a negative value of ∆S? (i) Ba2+(aq) + SO42-(aq) → BaSO4(s) (ii) 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) (iii) 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l) A. III only B. I and II C. II and III D. I only E. I and III

E. I and III

Consider the following system at equilibrium at 25°C: PCl3(g) + Cl2(g) <=> PCl5(g) for which ∆G° = -92.50 kJ. What will happen to the ratio of partial pressure of PCl5 to partial pressure of Cl2 as the temperature is raised? A. increases then decreases B. increases C. decreases then increases D. stays the same E. decreases

E. decreases PCl3(g) + Cl2(g) <==> PCl5(g) K = (PCl5) / (PCl3)(Cl2) ∆G = ∆Gº + RT ln K At equilibrium ∆G = 0, therefore ∆Gº = -RT ln K -92.50 = -RT ln K 92.50 / RT = ln K K will get smaller since T is in denominator

If a nucleus gains a neutron and then undergoes beta emission, A. its atomic number decreases by one and its mass number increases by one. B. its atomic number is unchanged and its mass number increases by one. C. both its atomic number and its mass number are unchanged. D. its atomic number increases by one and its mass number is unchanged. E. its atomic number increases by one and its mass number increases by one.

E. its atomic number increases by one and its mass number increases by one.

1 mole of NaCl(s) has a greater entropy than 1 mole of NaCl(aq). True or false True False

False

The process of a boulder rolling uphill is spontaneous. True or False? False True

False

The process of a cooked hamburger becoming raw is spontaneous. True or False? True False

False

The process of water decomposing to hydrogen and oxygen gases at room temperature and 1 atm pressure is spontaneous. True or False? False True

False

ΔS for the following reaction is positive. True or false? 2 H2(g) + O2(g) → 2 H2O(g) True False

False

ΔS for the following reaction is positive. True or false? HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) False True

False

The reduction potential for Ni 2+(aq) is -0.257 V and for O 2(g) is +0.695 V. The reaction below is spontaneous under standard conditions - true or false? Ni2+(aq) + H2O2(aq) → O2(g) + Ni(s) (in acidic solution)

False -2.57-.695 = neg so not spont

1 mole of CH3OH(l) has a greater entropy than 1 mole of C2H5OH(l). True or false False True

False Same physical state, more atoms more entropy

161 Tl is expected to be stable. 163Tl is expected to be stable.

False False only 205 & 204 Tl are stable

Co-55 undergoes positron decay. What is the product nucleus? Enter your answer using the same format, i.e, symbol-mass number

Fe-55

Consider the following half-reactions. Which of these is the strongest reducing agent listed here? I2(s) + 2 e- → 2 I-(aq), Eo = 0.53 V S2O82-(aq) + 2 e- → 2 SO42-(aq), Eo = 2.01 V Cr2O72-(aq) + 14 H+ + 6 e- → Cr3+(aq) + 7 H2O(l), Eo = 1.33 V I2(s) I-(aq) S2O82-(aq) SO42- Cr2O72- Cr3+(aq)

I-(aq) Lower Eo, stronger reducing agent I- is oxidized so it's reducing agent

Which of the following changes will increase the voltage of the cell Al(s)|Al3+(aq, 1.00 M )||Cu2+(aq,1.00 M)|Cu(s)? I. Increasing the surface area of the Al electrode II. Decreasing the concentration of Al3+(aq) to 0.001 M III. Decreasing the concentration of Cu2+(aq) to 0.001 M A. II only B. III only C. I and II only D. I only E. II and III

II. Decreasing the concentration of Al3+(aq) to 0.001 M Ecell = Eºcell - .059/n log[Al3+]/[Cu2+] decrease [Al3+], decrease log, increase Ecell

In the electrolysis of molten LiCl, which product forms at the cathode?

Li(l) Li+ is reduced

Fe-52 undergoes positron decay. What is the product nucleus? Enter your answer using the same format, i.e, symbol-mass number

Mn-52

Consider the Figure shown in which X represent Zn(s), T represents Co(s), and S is a solution that is 1.0 M in Co2+. The reduction potentials of Co2+ and Zn2+ are -0.27 V and -0.76 V, respectively. At which electrode does reduction occur?

T

Which letter labels the electrode at which reduction occurs in the figure shown? X Z S Y T see ss

T

ΔS for the following process is positive. True or false? A piece of wax melting. False True

True

Pa-232 undergoes beta decay. What is the product nucleus? Enter your answer using the same format, i.e, symbol-mass number

U-232

If the reaction is spontaneous as shown below, which letter labels the electrode that should be attached to the negative terminal of the voltmeter to read a positive voltage?

X

Consider the Figure shown in which X represents Zn(s), T represents Co(s), and S is a solution that is 1.0 M in Co2+. The reduction potentials of Co 2+ and Zn 2+ are -0.27 V and -0.76 V, respectively. In which direction do electrons flow in the external circuit? From S to Y from X to T from T to X Impossible to tell without further information! From Y to S

from X to T Co has a greater reduction potential -> cathode Zn is anode Electrons travel from anode to cathode

i) Stars like the sun generate energy through nuclear fusion. ii) The most stable nucleus in terms of binding energy per nucleon is 56Fe. iii) The core of nuclear fission reactors consists of uranium enriched in 235U surrounded by a moderator which slows down the neutrons from the 235U.

i)ii)iii)

If a nucleus undergoes beta particle emission

its atomic number increases by one and its mass number is unchanged

Which of the following statement(s) is/are correct? i) Nuclear fission was discovered when 238U was bombarded with alpha particles. ii) The control rods in nuclear fission reactors are composed of a substance that emits neutrons. iii) Electric power is widely generated using nuclear fusion reactors.

none of the choices

Identify the oxidizing agent and the reducing agent in the reaction. 3Cu(s) + 8H+(aq) + 2NO3-(aq) → 3Cu2+(aq) + 2NO(g) + 4H2O(l) oxidizing agent: H+ ; reducing agent: Cu oxidizing agent: NO3- ; reducing agent: Cu oxidizing agent: Cu ; reducing agent: NO3- oxidizing agent: NO3- ; reducing agent: H+

oxidizing agent: NO3- ; reducing agent: Cu