Old Quizzes

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 Old First Quizzes

First Quiz, 1998

1 - What are the SI units of pressure? (Give the answer in units of length, mass and time.)

2 - Calculate the value of the gas constant R in

a) L-bar/mol-K

b) meters3-bar/mol-K

(If you're suffering brain lock, and can't remember R in L-atm/mol-K or in J/mol-K, just ask and I'll sell one of them to you. Circle the units of the value you would like to purchase.)

First Quiz

Spring, 1997

1 - Calculate the density of CO2 at a pressure of 300 atm and a temperature of 400 K.

a) Using the ideal gas law, calculate the density in grams/L. (If you need it, I'll sell you the value of R.)

b) At these conditions, the compressibility factor, Z, of CO2 is 0.69. Calculate the density of carbon dioxide.

c) Are attractive or repulsive intermolecular forces stronger under these conditions?

Justify your answer.

d) Which density, the one in (a) or the one in (b), should be more accurate? Why?

(Note: You don't need to have calculated either density to answer this question.)

First quiz

Spring, 1995

1 - Consider the differential

3x2y2 dx + 2 xy3 dy.

Is this differential exact or inexact? Show why.

2 - Find the differential of the pressure of a Van der Waals gas, which has the equation of state:

(P + a/Vm2)(Vm - b) = RT. (Hint: first solve for the pressure, then find the differential.)

  Old Second Quizzes

Spring, 1995 

Two moles of O2, with _Cv = 20.8 J/mol-K, are warmed so quickly that q = 0 (an adiabatic process). The temperature is increased from 25.0 oC to 35.0 oC.

a) Calculate DU.

 b) Calculate DH.

 c) Is the gas being compressed or expanded? Explain, using the sign of the work as your clue.

Second Quiz

Spring, 1997

1 - Is the differential x2y dx + xy2 dy exact or inexact? Show your work.

2 - a) Write the most general equation for P-V work.

b) For a particular irreversible process, the work was 300 Joules.

i) Was the process an expansion or a compression? Explain your reasoning.

ii) What, if anything, can we say about the value of work if the process were carried out reversibly?

Second quiz

Spring, 1998

1 - Consider the differential

3 x2y2 dx + 2 xy3 dy.

Is this differential exact or inexact? Show why.

2 - An ideal gas expands from V1 = 1.00 L, P1 = 10.0 atm to V2 = 10.0 L, P2 = 1.00 atm, at a constant temperature of 25oC.

a) Calculate w if the external pressure is a constant 1.00 atm.

b) Calculate w if the process is reversible.

Old Third Quizzes

Quiz Number 3, 1996

Let's fiddle around with 2.00 moles of O2(g), assuming it behaves ideally. _Cv = 2.7R

The gas is expanded reversibly from 1.00 liters to 10.00 liters at a constant pressure of 10.0 atmosphere. The initial temperature is 60.9 K.

i) What is the final temperature? (If you can't do this, I'll sell you the final temperature.)

ii) Calculate DU.

iii) Calculate DH.

iv) Calculate w, in Joules.

Third Quiz, 1996

When one mole of methane, CH4, is burned in excess oxygen in a bomb calorimeter, 885.3 kilojoules of heat are evolved.

a) Determine DHcombustion for methane. Assume T = 298 K.

b) If the molar heat of formation of CO2 is -393.5 kJ/mole, and of water is -285.8 kJ/mole, use the data above to

Quiz Number 3, 1997

When 7.80 grams of benzene, C6H6, are burned in a bomb calorimeter, 327 kJ of heat are evolved. Assume the temperature is 25 oC. (Atomic weights: C: 12.0 g/mol; H: 1.0 g/mol)

a) Calculate the molar enthalpy of combustion of benzene, in kJ/mol.

b) Show, algebraically, how you could use the answer to (a) and the heats of formation of carbon dioxide and water to calculate the molar heat of formation of benzene.

Be as specific as possible; for instance, indicate by how much you would multiply each of the heats of formation in your calculation.

Third Quiz, 1998

When one mole of liquid methanol, CH3OH, is burned in excess oxygen in a bomb calorimeter, 726 kilojoules of heat are evolved.

a) Determine DHcombustion for methanol. Assume T = 298 K.

b) If the molar heat of formation of CO2 is -393.5 kJ/mole, and of water is -285.8 kJ/mole, use the data above to , use the data above to calculate the molar heat of formation of methanol.

Old Fourth Quizzes

Fourth Quiz, 1998

Let's play with 0.100 moles of helium, which we can assume behaves ideally. You should know the molar heat capacity of He, but I'll sell it to you if necessary. We'll start with 10.0 liters of He at 300K, and compress it using a constant pressure of 1.00 bar until the volume is 1.00 L and the final temperature is 350 K.

a) How much heat was absorbed or released by the gas?

b) If the process had been an irreversible adiabatic compression to 1.00 L, what would the final temperature have been?

c) (A quickie) Why does DH = (gamma)DU for the above processes?

Fourth Quiz, 1997

Consider the reaction, at 25oC.

pyruvate(aq) + 2 O2(g) = acetate(aq) + CO2(g) DHo = -297.3 kJ/mol

1 - Calculate DUo for the reaction, at 25oC.

2 - If DCP = 50.0 J/mol-K, calculate DHo for the reaction, at 37 oC.

Fourth Quiz, 1996

Let's fiddle around with an adiabatic process involving 2.00 moles of He, which we can assume behaves ideally. As you are undoubtedly aware, _Cv = (3/2)R for He and all other monatomic gases. Let's have the initial temperature be 300 K, and the initial volume be 10.0 liters. If the final temperature is 5.00 liters and the final temperature is 400K,

a) Calculate DH of helium.

b) Calculate the work done by the surroundings.

c) Calculate DSHe.

d) Was the process reversible, irreversible, or impossible? Use the second law to solve this problem. (If you couldn't do (c), assume the answer was DS = -3.0 J/K.)

Old Fifth Quizzes

Quiz No. 5, 1998

1 - Give an example of a spontaneous process for which DS is negative. Why doesn't this process violate the second law of thermodynamics?

 

2 - Consider all isothermal processes involving an ideal gas. Which of the following statements must be true? If so, show why. (Give an equation.) If not, give an example.

a) q = 0

b) DU = 0

c) DH = 0

d) DS = 0

e) DSuniverse = 0

Quiz Number 5, 1997

1 - Consider a reaction for which DHorxn = - 75.0 kJ/mol, and DSorxn = 250. J/mol-K.

a) Calculate the equilibrium constant for the reaction at 25oC.

b) Calculate Keq at 50oC, assuming DCP = 0.

c) Are your answers consistent with LeChatelier's Principle, which predicts how the equilibrium will shift if the temperature is changed? Explain.

Quiz number 5, 1996

Given the phase diagram,

P 900 *

r *

e 800 *

s *

s 700 *

u *

r 600 *

e *

(torr) 500 *

._______________________________________

500 600 700 800 900 1000

Temperature, oC

1 - Calculate the heat of sublimation of the substance.

2 - Derive the Clapeyron equation,

dP/dT = DH/(TDV)

3 - Use the Clapeyron equation to show which phase has the larger volume, the liquid or the solid.

Old Sixth Quizzes

Quiz number 6, 1998

1 - Given the plot of ln(Keq) vs 1/T,

a) Calculate the heat of reaction.

b) Calculate DSorxn

Quiz Number 6, 1997

1 - Use the Clausius - Clapeyron Equation to calculate the heat of vaporization of water if its vapor pressure is 23.76 torr at 25oC. Use the normal boiling point as your second point. (I, of course, will sell you the equation if necessary.)

2 - Let's assume the heat of vaporization of water is, say, 40,656 J/mole at its normal boiling point.

a) What is the numerical value of the Gibbs Free Energy of vaporization at this temperature and pressure? Why?

b) Use your results in (a) to calculate the molar entropy of vaporization at this temperature.

Sixth Quiz, 1996

a) If we dissolve 0.100 grams of a small protein in 500 grams of water at 25 oC, calculate the molecular weight of the protein if the solution exerts an osmotic pressure of 2.00 Pascal.

b) If a series of experiments gave the following results:

mass of protein/L 0.20 0.40 0.60

Calculated MW of 24000 23500 23000

the protein, g/mol

calculate the "best" value of the molecular weight of the protein.

Old Seventh Quizzes

 

Old Eighth Quizzes

1 - What's the Gibbs Phase Rule? Define each term.

2 - Draw the phase diagram for water and apply the Phase Rule to calculate the number of degrees of freedom at

a) the triple point.

b) 25oC and one bar pressure.

(Hint: in case you can't recall the answer to problem 1, you might be able to use your answer in problem 2 to help you. There's more than one way to pass a quiz.)

  Quiz Number 8

As you undoubtedly recall, the Nernst Equation, at 298K, is

E = Eo - (0.0592/n)log(Q)

1 - Consider two Standard Reduction Potentials, at 298K:

O2 + 4 H+ + 4 e- 6 2 H2O Eo = 1.229 volts

NAD+ + H+ + 2 e- 6 NADH Eo = - 0.113 volts

a) Calculate Eo, at 25oC, for the reaction

2 NADH + O2 + 2 H+ 6 2 H2O + 2 NAD+ {1.455 volts}

b) Now, calculate E* for the same reaction, still at 25oC. E* is the voltage with pH = 7, and all other species in their standard state. (If you couldn't do (a), assume your answer was, oh, 6.000 volts.) {1.041 V}

c) Finally, using either value of õo, calculate the voltage if the concentrations of all solutes were 0.10 moles/liter. (Have the pressure of O2 be its normal value in air.) {1.375 V}

Old Ninth Quizzes

Consider the enzyme catalyzed reaction: 2 S = P. If the proposed mechanism is

S + E = ES (forward rate constant k1, reverse rate constant k-1)

S + ES = E + P (where k2 is the rate constant.)

a) Using the steady state approximation for the intermediate, ES, derive an expression for [ES] as a function of [S], [E] and rate constants. {[ES] = k1[S][E]/(k-1 + k2[S])}

b) Assume that the rate of the last reaction is the overall rate of the reaction, and derive an equation for this rate, in terms of the concentrations of E and S, and rate constants. {rate = k1k2[S][E]/(k-1 = k2[S])}

c) If the rate is given by:rate = k[E][S]2/(1 + k'[S]), how could we force the reaction to be second order in S? {Make [S] very small.}

d) Under the conditions in c), what would be the rate determining step? Explain. {The last step}

1 - Consider the reaction

2 A + B = D + E

Run [A],moles/L [B],moles/L Rate,Moles/L-sec11 1 0.100 0.100 .000100

2 0.300 0.100 .00100

3 0.300 0.200 .000900

Calculate the parameters in the rate equation, to 3 significant figures.

{Order w.r.t. A: 2.10; w.r.t. B: -.152; kr = 0.0100 L/mol-sec}

2 - If the reaction above were 2nd order in A and zeroth order in B,

a) Predict a possible rate determining step.

{A + A = A2}

b) Construct a plausible mechanism.

{A + A = A2 (slow step)

A2 + B = D + E Fast step}

 

Consider an aqueous solution of sodium sulfate. There are lots (well, six) types of potential energy terms between the various molecules in the solution, e.g. ion - dipole, polarizability - dipole, etc.

For each of the ones that you can think of, write the type of energy (or force) that exists, an example of a pair of molecules that would be attracted by that form of potential energy, and write as much as you can recall about the form of the equation for the potential energy. This should include the power of r in the denominator, and what properties of the molecules that should be in the numerator.

Example:

Type of attraction Example Form of the equation

ion - dipole Na+ ... H2O Ep = - (Const.)(qNa+)(muH2O)cos(2)/r2

{ion - ion Na+ .Cl- E = Const(qNa)(qCl)/r

dipole - dipole H2O H2O E = - Const (muH2O)2/r4

ion - induced dipole Na+ . H2O

dipole - induced dipole H2O . H2O

dispersion H2O . H2O

Old Tenth Quizzes

1 - A certain reaction may proceed by a direct path or a catalyzed path.

If DS*path b = DS*path a + 40 J/mol-K, and

DH*path b = DH*path a + 20 kJ/mol,

a) Which path has the greater rate constant at 310 K, and by what ratio? (It is not necessary to calculate either rate constant!) {Path A; 19/1}

b) Which path is the catalyzed path? (a or b?) Explain. {Path A; lower EA)

2 - Consider the data for the reaction

A = B + C

time, sec 0 10 20 30 40 50

[A], M 0.200 0.143 0.111 0.092 0.077 0.067

a) Find the order with respect to A. {Second order}

b) Calculate the rate constant. (Units!) {0.25 L/mol-sec}

c) Calculate the concentration of A after 208 seconds.{0.0175 M}

d) Postulate a mechanism for the reaction, indicating the slowest step.

{A + A = A2 (RDS)

A2 = A + B + C}

1 - The energy of a one electron atom or ion with Z protons is given by the equation:

E = -Z2B/n2, where B = 2.18x10-18 Joules.

a) Calculate the wavelength of the photon emitted when an excited state electron on Li2+ falls from a 3d orbital to a 2p orbital. {Lambda = 72.9 nm}

b) Pretend DE in a) is 2.73x10-18 Joules. Use the Virial Theorem to calculate the change in potential energy of the electron during the process in a). {5.46x10-18 J}

Old Eleventh Quiz

  1 - Let's play with an approximate one-dimensional pib wavefunction, psi = N(L - x)x, where 0 > x > L.

a) Show that psi is normalized if N = (30/L5)2

b) If ^H = -(h/2(pi))2/2m)d2/dx2, is psi an eigenfunction of the Hamiltonian? Show why. {No, it's not.}

c) Use the average value postulate (Postulate 4) to calculate the average value of the energy. {5h2/4(pi)2mL2}

Old Twelfth Quiz

A bulb contains a mixture of gaseous ammonia and methane.

a) If the sample is irradiated (zapped) with photons having wavelengths around 0.10 cm, which molecules are likely to absorb the radiation? {ammonia}

b) What properties of the substances are necessary for absorption in a)? That is, what is the gross selection rule requirement? {The molecule must be polar.}

c) Now, we irradiate the samples with radiation having a wavelength of around 4.4x10-4 cm. Which molecules can absorb this radiation? {Both}

d) What molecular property is necessary (Again, what is the gross selection rule?) for absorption at this wavelength? {The dipole moment must change as the molecule vibrates.}

e) Which of the experiments (if either) will tell us the bond length in ammonia? {Both}