All India Institute of Medical Sciences 2007 M.B.B.S Chemistry Multiple Choice - Thermodynamics - Question Paper

1. For a process at 451 K and constant pressure, Ssurr is -326 J K-1. compute the volume of heat (in kJ) absorbed by the system.
2. Which of the subsequent produces an INCREASE in entropy of the system?
1. H2O(l) --> H2O(s)
2. 2O2(g) + 2SO(g) --> 2SO3(g)
3. 2CH3OH(g) + 3O2(g) --> 2CO2(g) + 4H2O(l)
4. I2(s) --> I2(l)
5. None of the above.
3. The gas-phase reaction ranging from H2 and Cl2 can be initiated by ultraviolet light at 25oC,

H2(g) + Cl2(g) --> 2HCl(g)

Using the thermodynamic data given below, compute the standard free energy change (in kJ) at 25oC for this reaction.

compound


Hfo, kJ mol-1


So, J mol-1 K-1

H2


0


130.57

Cl2


0


222.96

HCl


-92.307


186.80

4. In lecture, you observed the subsequent reaction,

2H2(g) + O2(g) --> 2H2O(g)

For this reaction, Ho = -241.8 kJ and So = -88.8 J K-1. Assuming that Ho = H and So = S at all temperatures, compute the temperature (in K) at which this reaction would become non-spontaneous.

5. For a particular chemical reaction at 400oC, G = -67 kJ. compute the time (in seconds) it will take for the reaction to reach completion.
6. For a particular chemical reaction, Ho is positive and So is negative. Which of the subsequent statements about the spontaneity of the reaction under standard conditions is TRUE?
1. The reaction will be spontaneous only if the magnitude of Ho is large enough to overcome the unfavorable entropy change.
2. The reaction will be spontaneous only if the magnitude of So is large enough to overcome the unfavorable enthalpy change.
3. The reaction will be spontaneous regardless of the magnitudes of Ho and So.
4. The reaction cannot be spontaneous.
5. The reaction will be spontaneous only of Go is positive.
7. Which of the subsequent is actual for an operating voltaic cell?
1. G > 0 ; E = 0
2. G < 0 ; E < 0
3. G = 0 ; E > 0
4. G = 0 ; E = 0
5. G < 0 ; E > 0
8. Which of the subsequent produces a reduce in entropy of the system? Hint: the system is shown in bold.
1. Dissolving sugar in a cup of coffee.
2. Condensation of water on the surface of a glass of iced tea on a hot summer day.
3. Boiling water in a pot on the stove to make spaghetti.
4. Allowing the liquid propane in a gas grill to escape from the tank.
5. Producing CO2 gas from baking soda (NaHCO3) when baking a cake.
9. Consider the subsequent reaction and thermodynamic data,

2H2O2(aq) <==> 2H2O(l) + O2(g)

substance


Hfo, kJ mol-1


So, J mol-1 K-1

H2O2(aq)


-191.17


143.9

H2O(l)


-285.83


69.91

O2(g)


0


205.14

compute the value (in kJ) of Go at 25oC.

10. For a particular chemical reaction, both Ho and So are negative. Which of the subsequent statements about the spontaneity of the reaction under standard conditions is TRUE?
1. The reaction will be spontaneous only if the magnitude of Ho is large enough to overcome the unfavorable entropy change.
2. The reaction will be spontaneous only if the magnitude of So is large enough to overcome the unfavorable enthalpy change.
3. The reaction will be spontaneous regardless of the magnitudes of Ho and So.
4. The reaction cannot be spontaneous.
5. The reaction will be spontaneous only of Go is positive.
11. The boiling point of a substance is the temperature at which equilibrium is established ranging from the liquid and the vapor.

CH3CH2OH(l) <==> CH3CH2OH(g)

compute the boiling point (in K) of ethanol, CH3CH2OH, if H = 42.6 kJ and S = 122 J/K for this process.

12. What is the significance of the 3rd legal regulations of Thermodynamics? select the best ans.
1. The absolute entropy of a substance reduces with increasing temperature.
2. The change in entropy of the universe must be positive for a spontaneous process.
3. The absolute value of entropy can be measured for a few very pure substances.
4. The change in entropy of the universe equals the sum of the change in entropy of the system plus the change in entropy of the surroundings.
5. The entropy of the universe is constant.
13. The Ksp for the sparingly soluble salt barium chromate (BaCrO4) at 25oC is equal to 2.0 x 10-10. compute Go (in kJ) for the subsequent reaction.

BaCrO4(s) <==> Ba2+(aq) + CrO42-(aq)

14. A Chemistry 116 learner determined the value of Ksp for a saturated solution of borax at several various temperatures. The value for So for the dissolution of borax in water can be determined from:
1. the slope of the line resulting from a plot of ln Ksp versus (1/T).
2. the y-intercept of the line resulting from a plot of ln Ksp versus T.
3. the slope of the line resulting from a plot of Ksp versus (1/T).
4. the y-intercept of the line resulting from a plot of ln Ksp versus (1/T).
5. the slope of the curve at 25oC from a plot of ln Ksp versus T.
15. Consider the subsequent gas-phase reaction,

2NO2(g) <==> 2NO(g) + O2(g), Go = +70.5 kJ

If 1.00 mole of NO2(g) is placed in a 1.00-L flask (no NO(g) or O2(g) initially) at 25oC, which of the subsequent statements is TRUE?

1. The reaction will occur spontaneously from left to right.
2. The reaction will occur spontaneously from right to left.
3. The reaction is not spontaneous in either direction.
4. The reaction is spontaneous in both directions.

Earning:   Approval pending.