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** Questions found on previous Second
Hour Exams; the answers are in curly brackets.**

** D stands for delta; for example, DH
represents delta H.**

** 1(15)- When the temperature is
increased from 298 K to 310 K, the equilibrium constant for a
particular reaction doubles. Calculate the value of DHo for the
reaction. {44.4 kJ/mol}**

** 2(15)- Calculate DG for the the
compression of 2.00 mol of CO2(g) from 0.100 atm to 200. atm at 400
K, **

** a) assuming CO2 behaves ideally.
{50.6 kJ}**

** b) using the fact that, for CO2, Pc
= 72.9 atm and Tc = 304 K. {(gamma = .72, 48.4 kJ}**

** 3(25)- The value of the Henry's Law
constant for CO2 in water at 298 K is k' = 1670 bar.**

** a) Calculate the mole fraction of
CO2 in water if the pressure of CO2 is 0.10 bar.**

** {.0000599}**

** b) Calculate D_Gmixing for the
solution in a). If you couldn't do (a), assume the mole fraction of
CO2 was 1.0x10-3. {-1.59, or -19.6 J}**

** c) What assumptions did you have to
make about the solution to do problem 3?**

** {Ideal dilute solution}**

** 4(20)- Consider the
reaction**

** H2(g, P = 0.1 bar) + Cl2(g, P = 100
bar) = 2 HCl(aq, 0.010 mol/kg) Eo = 1.615 volts**

** If the standard reduction potential
of Cl2 is 1.360 volts, and (gamma(0.010 molal HCl) = 0.905, calculate
the fugacity coefficient of Cl2. If necessary, I'll sell you the
standard reduction potential of H+aq). {gamma = 0.276}**

** 5(25)- Consider the following set
of concentrations vs. time, for the reaction**

** H2O2(g) = 2 OH(g)**

** time, minutes 0 10 20 30 40 50 60
70 **

** [A], moles/L 1.8 .98 .68 .51 .42
.35 .30 .26 **

** a) Predict the order of the
reaction. Explain. {second order}**

** b) Confirm your prediction. {k =
0.046 M-1min-1 (twice)}**

** c) What is the rate constant for
the reaction? { " }**

** d) Propose a rate determining step
for the reaction. { 2 H2O2 = H2O2 + H2O2*}**

** e) Propose an entire mechanism for
the reaction, using your RDS in d). {RDS, then **

** {H2O*2 = 2 OH}**

** Spring, 1992**

** R = 8.315 J/mol-K F = 96,487
coulombs/mole kB = 1.38x10-23 J/K**

** 1(32) - At 25oC, the vapor pressure
of pure bromine is 67.9 torr, and the vapor pressure of pure CCl4 is
33.9 torr. A solution with XBr2 = 0.100 has PBr2 = 1.35 torr and
PCCl4 = 33.0 torr. **

**a) Calculate DG when 10.0 moles of
bromine are mixed with 90.0 moles of CCl4. {-103 kJ}**

** b) Calculate both activity
coefficients for the solution in a). {1.08, 0.199} **

** c) Would you expect DH for the
process in a) to be positive, negative, or zero? Why?
{damfino}**

** d) If, for CCl4, the cryoscopic
constant is -4.0 oC/molal solution, and the normal freezing point is
-23.0 oC, calculate the freezing point of the solution in a).{-25.9
oC} **

** e) Estimate the molar heat of
fusion of CCl4. {20.0 kJ/mol}**

** Kf = -R(To)2(MWA)/(DHfus.1000g/kg)
**

** 2(20) - Consider the reaction Cu2S
= 2 Cu+(aq) + S2-(aq) Ksp = 1.6x10-48**

** a) Calculate the solubility of Cu2S
in water. {7.4x10-17 M}**

** b) Calculate the solubility of Cu2S
in 0.10 M NaNO3. {1.6x10-16 M}**

** c) Calculate DGo for the reaction
at 25oC. {273 kJ/mol}**

** 3(16) - Two compartments are
separated by a membrane that is permeable to Na+ and Cl-,
but**

**not to a protein, P+10. Initially, the
right compartment contains 0.0100 M NaCl, and the left**

**compartment contains 0.0100 M NaCl and
0.0010 M PCl10, which ionizes completely in water.**

** a) Calculate the concentration of
Cl- in each compartment at equilibrium.{.0080,.012}**

** b) Use the equilibrium
concentrations of Cl- to calculate the Nernst potential,**

** Mright - Mleft, at 25oC. {-10.4 mV}
**

** 4(10) - A cell has Eo = 0.200 volts
at 25.00oC and Eo = 0.210 volts at 30.00oC.**

** Estimate DS for the cell reaction
if three moles of electrons are transferred. {580J/K}**

** 5(14) - The first vibrational
excited state of Br2(g) is 400 cm-1 (8.0x10-21 J) above the
ground**

**state. Calculate the ratio of the number
of molecules in the first excited state, compared to the**

**number of molecules in the ground state,
(N1/N0), at 25oC.{0.143}**

** Second Hour Exam Spring, 1994 F =
96,487 coulombs/mol**

** 1(18) - As everyone who has had
general chemistry knows, at 25 oC,**

** H2O(l) W H+(aq) + OH-(aq), Kw =
1.0x10-14**

** We also showed that, at 100 oC, Kw
= 9.2x10-13.**

** a) Calculate DHorxn. {55.8 kJ/mol}
**

** b) Calculate DSorxn. {-81.0 J/mol}
**

** c) Is the sign of DSorxn
intuitively correct? That is, did it have the sign you expected? Why
or why**

**not? (If you couldn't do (b), what you
think the sign should be, and why?)**

** 2(20) - a) Show that (dS/dV)T =
(dP/dT)V. Start with the appropriate state function, not
its**

**differential.**

** b) For a Van der Waals gas, (P +
an2/V2)(V - nb) = nRT.**

** Derive the expression for (dS/dV)T
for this gas. {nR/(V - nb)}**

** c) Show that DS = nRln{(V2 -
nb)/(V1 - nb)}**

** 3(18) - a) Why are we justified in
using mu = muo + RTln(PA/PoA) for solvents, rather than mu
=**

**muA + RTln(fA/foA)?**

** b) Consider EtOH, dissolved in
acetone. If the mole fraction of EtOH is 0.20, and gammaEtOH
=**

**1.20, **

** i) calculate the activity of ETOH.
{0.24}**

** ii) calculate the vapor pressure of
EtOH, if the vapor pressure of pure EtOH is 32.0 torr.
{7.68**

**torr}**

** 4(14) - a) The ratio of the
concentration of K+ inside a cell to that outside a cell is 20/1.
Calculate**

**Einside - Eoutside at 37 oC. {- 0.0800
V}**

** b) If Ein - Eout = - 0.020 volts,
was K+ actively transported into or out of the cell? Explain. {into}
**

** 5(10) - Derive the Nernst equation,
starting with two equations for DGrxn.**

** Chemistry 142 Second Hour Exam
Spring, 1995**

** 1(23)- Consider one of my favorite
reactions:**

** H2O(l) = H+(aq) + OH-(aq) Kw =
1.0x10-14 at 298 K.**

** Also, DHo = 55.8 kJ/mol, and can be
presumed to be constant.**

** (6) a) Calculate the equilibrium
constant at 310 K. {2.4x10-14}**

** (4) b) Calculate the pH at 310 K.
{6.81}**

** (8) c) Calculate DSo for the
reaction. {-80.8 J/K}**

** (5) d) Rationalize the sign of DSo.
(Explain why it has the sign that it does. If you couldn't do
c),**

**assume that DSo is negative.)**

** 2(23) The vapor pressures of pure
methanol and pure water at 21 oC are 100 and 18.7 torr,**

**respectively. The vapor over a solution
containing 48.0 g CH3OH and 32.4 g H2O has**

**P(CH3OH) = 40.2 torr and P(H2O) = 9.21
torr.**

** (10) a) Calculate the activity and
activity coefficient for each component in the solution.**

** {.493,.402,.904,.884}**

** (8) b) Calculate DGmixing for this
(non-ideal!) solution. {- 6542 J}**

** (5) c) Do you expect the mixing
process for this solution to be exothermic or endothermic?**

**Explain. {Exo} **

** 3(10) - The molar conductivity at
infinite dilution, (Lambda)o, for potassium chloride is
149.9**

**cm2/mol-ohm. If the ionic mobilities of
K+ and Cl- are 0.000762 and 0.000791 cm2/volt-sec**

**respectively, calculate the individual
molar conductivity at infinite dilution of each ion.**

** {for K+, 73.6; for Cl-, 76.3
cm2/mol-ohm}**

** 4(25) - Consider the reduction of
acetaldehyde to ethanol (yay!) by NADH:**

** CH3CHO(aq) + NADH(aq) + H+(aq) =
C2H5OH(aq) + NAD+(aq)**

** At 298 K, Eo = 0.330 volts, and at
310 K, Eo = 0.333 volts.**

** (10) a) Calculate an approximate
value of DSo for the reaction. {50 J/K}**

** (8) b) If all solutes except H+ are
at a concentration of 0.0010 molar, and the pH is 7.0, **

** calculate E at 298 K. {0.123
V}**

** (6) c) Technically, the constant
"0.0592 volts" in the Nernst equation is incorrect at
temperatures**

**differing from 298 K. What would be a
more accurate constant at 310K? {0.0616 volts}**

** 5(20) - Consider the isomerization
of cyclopropane: cyclo-C3H6(g) 6 CH3CH=CH2(g)**

** time, minutes 0 10 20 30 40 50 60
**

** [cyclo-C3H6]/10-3M 1.00 0.67 0.50
0.40 0.33 0.28 0.25**

** (6) a) Determine the order of the
reaction with respect to cyclopropane. {second}**

** (4) b) What is the rate constant?
{50 L/mol-min} **

** (5) c) Propose a Rate Determining
Step for the reaction. {2 C3H6 = C3H6* + C3H6}**

** (5) d) Propose a mechanism for the
reaction. {The RDS, followed by C3H6* = C3-CH=CH2**

** Second Hour Exam Spring, 1996 F =
96,487 coulombs/mol **

** 1(25) - Let's see how water likes
having some sucrose mixed in with it. At 20oC, the vapor**

**pressure of pure water is 17.54 torr.
After we toss 0.400 moles of sugar into 100 grams of
water,**

**the vapor pressure of the solution is
15.89 torr.**

** a) Calculate the activity of water
in the solution. {0.9059}**

** b) Calculate the activity
coefficient of water in the solution. {0.971}**

** c) Calculate DGmixing for water.
{-13.5 kJ}**

** d) Would you guess that the heat of
solution of sugar in water would be positive or negative?**

**Why? {negative}**

** e) Should you have any reservations
about your answer in d)? Why? {Sure!} **

** 2(14) - a) What fraction of the
total current is carried by Na+ when a current flows through
an**

**aqueous solution of NaBr at 25oC? The
limiting molar ionic conductivity of Na+(aq) and Br-(aq)**

**are 50.1 S cm2/mol and 78.1 S cm2/mol,
respectively.{.391}**

** b) Would the conductivity of a NaBr
solution go up or down if the concentration of the salt
were**

**increased? Why? {up}**

** c) Would the molar conducivity of
the solution increase or decrease if the concentration
were**

**increased? What evidence do you
have/remember? {decrease}**

** 4(46) - Consider the reaction, at
25oC.**

** 2 Fe(s) + 3 Co2+(aq) = 2 Fe3+(aq) +
3 Co(s)**

** If the standard potential for the
reaction is Eo = 0.1955 + 0.00015(T) volts,**

** a) Calculate the standard potential
for the cell. {0.240 V}**

** b) Calculate the Standard Reduction
Potential (SRP) for cobalt if the SRP**

** for iron(III) is -0.0402 volts.
{0.200 V}**

** c) Calculate DGo for the reaction.
{-139 kJ}**

** d) Calculate DSo for the reaction.
{86.9 J/K}**

** e) Calculate E for the reaction in
a solution of 0.10 molar Fe(NO3)3 and 0.010 molar**

**Co(NO3)2, assuming ideality. {0.279
V}**

** f) Calculate the ionic strength of
the solution. {0.063}**

** g) Using the DHLL equation,
calculate the ionic activity coefficient of each metal
ion.**

** {0.414 for Fe(III), 0.444 for
Co(II)} **

** h) Assuming the results from (g)
were (gamma = 0.50, calculate the voltage of the rxn.
{.243V}**

** 1(15)- The change in Gibbs Free
Energy when 2.00 moles of O2 is compressed from 0.100 bar**

**to 200. bar at 298 K is 36.6 kJ.
**

** (10) a) Calculate the fugacity of
oxygen at 200 bar, 298 K. {161 atm}**

** (5) b) Calculate the fugacity
coefficient of oxygen at these conditions. {.806}**

** 2(27)- The vapor pressure of pure
CCl4 is 39.345 kPa at 20 oC. When 1.00 mol CCl4 is mixed**

**with 4.00 mol C3H8O (acetone), the
activity coefficient of CCl4 is 1.10.**

** (9) a) Calculate the activity of
CCl4. {.220}**

** (9) b) Calculate the vapor pressure
of CCl4. {8.66kPa}**

** (9) c) Calculate the change in
Gibbs Free Energy of CCl4 when it was mixed with acetone.**

**{-3690 J}**

** 3(58)- Consider the reaction at 298
K:**

** 2 AgCl(s) + Cu(s) = 2 Ag(s) +
Cu2+(aq) + 2 Cl-(aq) DHorxn = - 16.41 kJ/mol**

** Here are some useful data:
**

** AgCl(s) + e- = Ag(s) + Cl-(aq) Eo =
0.2224 Volts**

** Cu2+(aq) + 2 e- = Cu(s) Eo = 0.337
Volts**

** (8) a) Calculate Eorxn {- 0.115 V}
**

** (8) b) Calculate the equilibrium
constant for the reaction. {.000129}**

** (8) c) Calculate DSo for the
reaction. {-130J/mol-K}**

** (10) d) Use your answer in (c) to
estimate the value of Eorxn at 350 K. {-0.150 V}**

** (If you couldn't do (c), pretend
)So = - 120 J/K)**

** e) Let [CuCl2] = 0.010 M
**

** (8) i) Calculate Erxn at 298 K,
assuming all activity coefficients are unity. {0.045 V}**

** (8) ii) Calculate the mean ionic
activity coefficient of the 0.010 M CuCl2 solution.(.666)**

** (8) iii) Calculate Erxn at 298 K,
using your answer in (ii). {0.061 V}**

** As usual, if you need a specific
equation, just ask. Also, if you need an answer to an early
question**

**in order to proceed, either give a good
guess (and indicate that's what you're doing), or ask for**

**one.**

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