The City College of New York Chemistry Department Chemistry 10401, Sections H* , Spring 2014 Prof. T. Lazaridis Final examination, May 19, 2014 Last Name:____________________________ First Name: _______________________ Instructions: There are 15 questions in this exam, check both sides of the sheets * Do not cheat.
You will automatically fail and may face further action. * You may tear off the last sheet, which
contains the periodic table, and use it as scrap paper. Anything written on it will not be counted
during grading. * Use a calculator. No cellphones or devices for email/texting. * Please do not
leave the room during the exam. If you must go to the bathroom, please give the exam to the
Professor. * Place your student ID on the desk in front you.
To guarantee full marks, you must SHOW WORK/REASONING, even for multiple choice
questions. No work or reasoning means no points.
Constants: 8
-­‐34
Speed of light : 2.9979 X 10 m/s Planck's constant : 6.626 X 10 Js Nav: 6.022X1023 F=96485 C/mol e R= 0.0821 L atm/mol K = 0.083145 bar L/mol K =8.3145 J/mol K = 62.364 L torr/mol K Data: Absolute entropies (So, J/K) : NO:210.76, N2: 191.61, O2: 205.138 Standard enthalpies of formation (ΔHfo, kJ/mol): NO: 90.25 Equations: ΔTf=-­‐KfXm ΔTb=KbXm 1st order: t1/2= ln2/k ln(A/Ao)=-­‐kt 2nd order: 1/A=1/Ao+kt k=Aexp(-­‐Ea/RT) Kp=Kc(RT)Δn ΔGo=-­‐RTlnK ΔG= ΔGo +RTlnQ pH=pKa + log [base]/[acid] Eocell = (0.025693 V/z ) ln K = (0.0592V/z) log K Ecell = Eocell – (0.0592V/z) log Q ΔGo=-­‐zFEo Score: 1._____ 2._____ 3._____ 4._____ 5._____ 6._____ 7._____ 8._____ 9._____ 10._____
11.____ 12._____ 13._____ 14.____ 15._____
Total: _____
1. (6) Consider dimethyl ether (CH3-O-CH3) and ethanol (CH3CH2OH).
a. (2) Which intermolecular forces do you expect between dimethyl ether molecules?
b. (2) Which intermolecular forces do you expect between ethanol molecules?
c. (2) Which of the two liquids do you expect to have lower vapor pressure? Explain.
2. (6) The freezing point of a solution containing 0.286 g of an unknown substance in
25.0 g of benzene is 5.17 oC. Calculate the molar mass of the unknown. (Tf of pure
benzene is 5.53 oC and Kf = 4.90 oC/m)
3. (6) The rate constant for a reaction is 0.522 M-1s-1 at 592 K and the activation energy is
1.00X105 J/mol. What is the rate constant at 627 K?
4. (7) Consider the formation of HI from its elements: H2 (g)+I2 (g) à 2HI (g)
The following mechanism has been proposed for this reaction:
I2 (g) ⇌ 2I (g)
H2 (g) + 2I (g) à 2HI (g)
fast
slow
Derive the rate law for this reaction. What is the overall order of the reaction?
5. (7) A 1.00-mol sample of PCl5 is placed in a 10.0-L flask and allowed to come to
equilibrium at 250 oC:
PCl5 (g) ⇌ PCl3 (g) + Cl2 (g)
If the amount of chlorine in the equilibrium mixture is 0.470 mol, calculate
a) (3) the equilibrium concentration of each gas
b) (2) Kc
c) (2) Kp
6. (7) Calculate the pH of each of the following solutions
a. (1) 0.015 M HCl
b. (2) 0.025 M KOH
c. (4) 0.100 M hydroxylamine, which ionizes as follows:
NH2OH (aq) + H2O ⇌ NH3OH+ (aq) + OH- (aq)
Kb=1.0X10-8
7. (7) a. (4) Calculate the pH of a solution containing 0.10 M NH3 and 0.25 M NH4Cl (Kb
for ammonia is 1.8X10-5).
b. (3) Calculate the pH after 1.00 L of the above solution absorbs 0.02 mol of HCl gas
8. (7) HCN is weak acid with Ka=4.93X10-10. What will be the pH of a 0.10 M KCN
solution?
9. (6) Will a precipitate form when equal volumes of 2.0X10-3 M Pb(NO3)2 and 2.0X10-3
M NaCl are mixed? (Ksp of PbCl2 is 1.7X10-5).
10. (8) At 25oC, Kp=98.4 for the reaction 2NO (g) + Br2 (g) ⇌ 2NOBr (g)
a. (3) Calculate the standard free energy at 25 oC
b. (3) Calculate the free energy of this reaction at 25 oC when the partial pressures of
NO,Br2, NOBr are 0.20, 0.50, 0.30 bar, respectively.
c. (2) Is the reacting system closer to equilibrium under the conditions of part b or under
standard-state conditions?
11. (5) Use data on the front page to calculate the Kp of the following reaction at 25 oC.
N2 (g) + O2 (g) ⇌ 2NO (g)
12. (7) The standard free energies of formation of Hg2+ (aq) and Hg22+ (aq) are +164.4
and +153.5 kJ/mol, respectively. Calculate Eo for a galvanic cell that utilizes the reaction
Hg2+ (aq) + Hg (l) à Hg22+ (aq)
(Hint: the oxidation half reaction is 2Hg(l)à Hg22+ (aq) + 2e-)
13. (7) A standard Ni/Ni2+ half-cell is coupled with a Ni/Ni2+ half-cell in which the Ni2+
concentration is 0.015 M. What will be the potential of this cell?
14. (8) Draw orbital diagrams and determine the number of unpaired electrons in the
following complex ions:
a) (4) Ni(NH3)62+
b) (4) low spin (strong field) Pt(NH3)3Cl3+
15. (6) Complete the following nuclear equations by adding missing symbols, mass
numbers, and atomic numbers:
a) (3) 98Mo + 2H à ? + a neutron
b) (3) ? + a proton à 21Mg + 3 neutrons