Thermodynamic Final Exam Review

Physical Chemistry Thermodynamics Practice Exam

Montana Tech Name ____________________

There is a periodic chart and a list of constants at the end of this exam.

NO2 would behave most like an ideal gas at:

a. 25 °C and 0.5 atm b. 25 °C and 1 atm

c. 75 °C and 0.5 atm d. 75 °C and 1 atm

The temperature and volume of a fixed amount of an ideal gas are doubled. The density of this gas is:

a. quartered b. halved

c. unchanged d. doubled

e. quadrupled

Two flasks of equal volume, containing an ideal gas, are connected by a tube of negligible volume. One flask is at 27 °C and the other flask is at 127 °C. Circle all the statements which are true.

a. The pressure of the gas in the warmer flask is equal to the pressure of the gas in the colder flask.

b. The density of the gas in the colder flask is less than the density of the gas in the warmer flask.

c. The mass of the gas in the warmer flask is greater than the mass of the gas in the colder flask.

d. The number of moles of gas in the colder flask is smaller than the number of moles of gas in the warmer flask.

Which of the following gases is behaving least like an ideal gas at a given T & P:

a. CO2 b. SO2

c. SeO2 d. TeO2

e. PoO2

A gas whose critical pressure is 4.0 bar is at 2.0 bar of pressure. What is the reduced pressure of this gas?

a. 0.25 b. 0.50

c. 2.0 d. 4.0

e. 8.0

At low pressures and temperatures below its critical temperature a real gas has a compressibility factor, Z, less than 1, because:

a. intermolecular forces are pulling the molecules together.

b. the molecules of finite volume are beginning to bump into each other.

c. the gas cannot condense into a liquid above its critical temperature.

d. its pressure is above its critical pressure

Which of the following gases would have the smallest average speed:

a. F2 at 25.0 °C b. O2 at 25.0 °C

c. O2 at 50.0 °C d. NH3 at 50.0 °C

In a collection of molecules in the gas phase what is the relative relationship between the mean speed, cmean, the root mean squared speed, crms, and the most probable speed, cmp?

a. cmean > crms > cmp b. cmean > cmp > crms

c. crms > cmean > cmp d. cmp > crms > cmean

e. cmp > cmean > crms

For an ideal gas the value of the partial derivative:

(∂E/∂V)T = ?is:

a. Cp b. Cv

c. 5/2 R d. 3/2 R

e. 0

For a monatomic ideal gas the value of the partial derivative:

(∂H/∂T)P = ?is:

a. Cp b. Cv

c. 5/2 R d. 3/2 R

e. 0

For a real gas the value of the partial derivative:

(∂H/∂T)P = ?is:

a. Cp b. Cv

c. 5/2 R d. 3/2 R

e. 0

One mole of an ideal gas is heated from T1 to T2 at constant volume. The constant pressure heat capacity for this gas is:

Cp = a + b T + c T - 2

Which expression listed below should be used to calculate the change in enthalpy:

a. (a – R) (T2 – T1) + b/2 (T2 – T1)2 + c/3 (T2 – T1)3

b. (a – R) (T2 – T1) + b/2 (T22 – T1

2) – c (1/T2 – 1/T1)

c. (a – R) (T2 – T1) + b/2 (T22 – T1

2) + c/3 (T23 – T1

3)

d. a (T2 – T1) + b/2 (T22 – T1

2) + c/3 (T23 – T1

3)

e. a (T2 – T1) + b/2 (T22 – T1

2) – c (1/T2 – 1/T1)

Which one of the following expressions should be used to calculate the heat transferrequired to cool an ideal gas at constant volume (choose the best answer):

a. ∫ Cp dT b. ∫ Cv dT

c. ∫ (Cv + n R) dT d. ∫ 5/2 n R dT

e. none of the above

Which one of the following expressions should be used to calculate the energy change when cooling an ideal gas at constant pressure (choose the best answer):


c. ∫ (Cv + n R) dT d. ∫ 5/2 n R dT


Which one of the following expressions should be used to calculate the enthalpy change when cooling a polyatomic gas at constant pressure (choose the best answer):


c. ∫ ( Cp - n R) dT d. ∫ 5/2 n R dT

e. none of the above The isothermal compressibility, , for an ideal gas is equal to:

a. 1 / P b. – 1 / P

c. 1 / T d. –


A fixed amount of an ideal gas initially at V1 and T1 is taken through the following three step cyclic process:

step 1: The gas is cooled at constant volume until its temperature is T2.

step 2: Then the gas is isothermally and reversibly expanded. During this expansion 1,076 Joules of heat are transferred to the gas.

step 3: Finally the gas is adiabatically compressed back to its original volume and temperature. During this compression 1,247 Joules of work are done on the gas.

Complete the following table (hint: it may help to diagram this cyclic process on PV diagram):

heat work Estep 1step 2

step 3 total

For the next five questions select the letter corresponding to the best answer from among the following choices:

a. ∆E = 0 q = 0 w = 0

b. ∆E = 0 q > 0 w < 0

c. ∆E = 0 q < 0 w > 0

d. ∆E > 0 q > 0 w = 0

e. ∆E > 0 q > 0 w < 0

f. ∆E > 0 q < 0 w > 0

g. ∆E > 0 q = 0 w > 0

h. ∆E < 0 q < 0 w = 0

i. ∆E < 0 q > 0 w < 0

j. ∆E < 0 q < 0 w > 0

k. ∆E < 0 q = 0 w < 0

An ideal gas is compressed adiabatically:

An ideal gas is expanded isothermally:

An ideal gas is heated isobarically:

A real gas is warmed isometrically:

A real gas is cooled adiabatically:

If the enthalpy of combustion of octane at 25 °C is ΔH;

C8H18 (l) + 25/2 O2 (g) -------------> 8 CO2 (g) + 9 H2O (l)

the internal energy, ΔE of combustion is:

a. ΔH b. ΔH + 9/2 R T

c. ΔH - 9/2 R T d. ΔH + 7/2 R T

e. ΔH - 7/2 R T

Which of the following reactions is associated with the standard molar enthalpy of formation of carbon dioxide:

∆H°f, 298 K [SO2 (g)] = – 296.81 kJ/mole

a. SO (g) + ½ O2 (g) –––––> SO2 (g)

b. SO2 (g) –––––> S (s) + O2 (g)

c. S (g) + O2 (g) –––––> SO2 (g)

d. S (s) + O2 (g) –––––> SO2 (g)

Which of the following reactions is associated with the integral heat of formation at infinite dilution of solid gypsum, CaSO4•2H2O (s):

∆H∞soln, 298 K [CaSO4•2H2O (s)] = - 483.06 kcal/mole

a. CaSO4•2H2O (s) + ∞ aq –––––> Ca2+ (∞ aq) + SO42- (∞ aq)

b. Ca2+ (∞ aq) + SO42- (∞ aq) –––––> CaSO4•2H2O (s) + ∞ aq

c. Ca2+ (∞ aq) + SO42- (∞ aq) + 2 H2O (l) –––––> CaSO4•2H2O (s) + ∞ aq

d. CaSO4•2H2O (s) + ∞ aq –––> Ca2+ (∞ aq) + SO42- (∞ aq) + 2 H2O (l)

e. Ca (s) + S (s) + 2 H2 (g) + 3 O2 (g) + ∞ aq –––––> CaSO4•2H2O (∞ aq)

Which of the following reactions is associated with the bond enthalpy ofthe osygen oxygen double bond in O2:

∆H O2 = + 495 kJ/mole

a. ½ O2 (g) –––––> O (g)

b. O (g) + O (g) –––––> O2 (g)

c. O2 (g) –––––> 2 O (g)

d. O (g) –––––> ½ O2 (g)

e. O2 (l) –––––> O2 (g)

Using the reaction data:

2 P (s) + 3 Cl2 (g) -----> 2 PCl3 (l) Ho = - 151.8 kcal

PCl5 (s) -----> PCl3 (l) + Cl2 (g) Ho = + 32.81 kcal

calculate the enthalpy change for the reaction:

P (s) + 5/2 Cl2 (g) ------> PCl5 (g)

a. - 43.1 kcal b. - 108.7 kcal

c. - 119.0 kcal d. - 184.6 kcal

e. - 217.2 kcal

Gibb’s free energy, G, is defined as:

a. G = E + P V b. G = H + P V

c. G = H - P V d. G = H + T S

e. G = H - T S

The total differential for the Gibb’s free energy, G, is:

a. dG = P dV – S dT b. dG = V dP - T dS

c. dG = T dS - P dV d. dG = P dV - T dS

e. dG = V dP - S dT

Complete the Maxwell relation:

- (S / P)T = ?

a. (V / S)P b. (T / V)P

c. (P / T)V d. (V/ T)P

e. (P / S)T

Complete the relation:

(G / P)T = ?

a. - S b. V

c. (G / T)P d. (V / T)P

e. - (S / P)T

1000 kcal of heat are withdrawn from a high temperature reservoir and used by the system to do 268 kcal of work on the surroundings. The amount of waste heat transferred to a lower temperature reservoir is:

a. - 1268 kcal b. - 732 kcal

c. 0 kcal d. + 732 kcal

e. - 732 kcal

What is the thermodynamic efficiency of an engine running at 60 °C and which is cooled by water at 15 °C ?

a. 14 % b. 16 %

c. 25 % d. 75 %

e. 86 %

5 molecules are distributed between two gas bulbs. What is the probability that three of the molecules will be found in one of the bulbs and two in the other?

a. 0.03 b. 0.17

c. 0.31 d. 0.40

e. 0.62

For which of the following processes is the entropy change for the system, ∆Ssystem zero:

a. an ideal gas expands isothermally

b. an ideal gas isothermally expands into a vacuum

c. an ideal gas expands adiabatically and irreversibly

d. two ideal gases are mixed to form an ideal solution


The next three questions refer to the following figure in which an ideal gas is isothermally expanded:

The entropy change for the gas, ∆Sgas, is:

a. < 0 b. > 0

c. = 0 d. insufficient informationis provided to answer

The entropy change in the surroundings, ∆Ssurr, is:

a. < 0 b. > 0


The total entropy change, ∆Stotal, is:

a. < 0 b. > 0


The next five questions refer to the phase change:

60.0 °C

C6H6 (l) –––––––> C6H6 (g)

1 bar

The equilibrium boiling point of benzene at 1 bar is 80.1 °C. The system is in contact with an isothermal surroundings at 60.0 °C.

The entropy change for the benzene, ∆Sbenzene, is:

a. > 0 b. = 0

c. < 0 d. insufficient informationis provided to answer

The total entropy change, ∆Stotal, is:

a. > 0 b. = 0


The entropy change for the surroundings, ∆Ssurr, is:

a. > 0 b. = 0


The Gibb's free energy change for the benzene, ∆G 60.0 °C, benzene is:

a. > 0 b. = 0


The standard Gibb's free energy change for the benzene, ∆G° 80.1 °C, benzene, is:

a. > 0 b. = 0


For the vaporization of benzene at standard pressure:

C6H6 (l) --------> C6H6 (g)

ΔHvap = + 33.9 kJ / mole ΔSvap = + 96.0 J / (mole K)

Estimate the equilibrium boiling point at standard pressure:

a. 2.8 K b. 273.2 K

c. 298.2 K d. 353.2 K

c. 2832 K

The standard Gibb's free energies of formation of calcite and aragonite, two crystalline forms of CaCO3 (s), are:

∆G°f, 298 K (kcal/mole)

CaCO3 (s, calcite) – 269.78

CaCO3 (s, aragonite) – 269.53

At 25.0 °C and standard pressure:

a. calcite is stable

b. aragonite is stable

c. calcite and aragonite are at equilibrium

d. insufficient information is provided on which to base an answer

When the temperature on a substance is decreased isobarically the Gibb's free energy of the substance:

a. increases b. decreases

c. doesn't change d. can either increase or decrease depending on the situation

When the pressure on a substance is decreased isothermally the Gibb's free energy of the substance:

a. increases b. decreases

c. doesn't change d. can either increase or decrease depending on the situation

50.0 mL each of liquid benzene, C6H6 (l), and liquid toluene, C6H5CH3 (l) are mixed at 25.0 oC and 1.00 bar. Which of the following quantities are expected to be zero (circle all that apply)?

a. V b. E

c. H d. S

e. G f. Go

2.000 moles of A and 1.000 of B and 1.000 of oC come to equilibrium in a 1.000 L constant volume container and at a constant temperature of 150 oC:

A (g) + 2 B (g) --------> 2 C (g)

At equilibrium there are 2.250 moles of A in the mixture. What is Kc for the reaction at 150 oC?

a. 0.04938 b. 0.1482

c. 0.1600 d. 0.5000

e. 20.25

Useful information:

R = 0.08205 l atm/mole K = 8.314 J/mole K = 1.987 cal/mole K

1.000 atm = 14.696 atm

1.000 atm = 760.0 torr

1.000 lbm = 453.6 grams

K = oC + 273.15

oR = oF + 459.67 K

Avogadro's number = 6.023 x 1023

1.000 in. = 2.54 cm

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Thermodynamic Final Exam Review