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| 1 | |
Which of the following substances has the lowest standard molar entropy (S°) at 25°C? |
| | A) | CH3OH(l) |
| | B) | CO(g) |
| | C) | MgO(s) |
| | D) | H2O(l) |
| | E) | CaCO3(s) |
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| 2 | |
Select the correct statement of a law of thermodynamics. |
| | A) | The enthalpy of the universe is constantly increasing. |
| | B) | The entropy of the universe is constant. |
| | C) | The entropy of an element in its standard state at 25°C is zero. |
| | D) | Every spontaneous process is accompanied by an increase in total entropy. |
| | E) | Every spontaneous process is accompanied by a decrease in the enthalpy of the system. |
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| 3 | |
Calculate ΔSº for the following reaction:
4Cr(s) + 3O2(g) →
2Cr2O3(s)
Data: Standard molar entropies, Sº (J/mol.K): Cr(s), 23.8; O2(g), 205.1;
Cr2O3(s), 81.2 |
| | A) | 548.1 J/K |
| | B) | 147.7 J/K |
| | C) | -147.7 J/K |
| | D) | -548.1 J/K |
| | E) | -66.5 J/K |
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| 4 | |
Consider the reaction:
4NH3(g) + 3O2(g) →
2N2(g) + 6H2O(g)
For this reaction, ΔSº is +128.2 J/K. Use this value and the following standard molar entropies to calculate the standard molar entropy of NH3(g).
Sº (J/mol•K): O2, 205.0; N2, 191.5; H2O, 188.7 |
| | A) | 193 J/mol•K |
| | B) | 95.8 J/mol•K |
| | C) | 383.0 J/mol•K |
| | D) | 0 J/mol•K |
| | E) | 47.0 J/mol•K |
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| 5 | |
When crystalline solid barium hydroxide octahydrate and crystalline solid ammonium nitrate are mixed in a beaker at room temperature, a spontaneous reaction occurs. The temperature of the beaker contents rapidly falls to below 0°C. Use this information to decide whether the reaction is exothermic or endothermic and what the signs of ΔH and ΔS are. |
| | A) | endothermic; ΔH > 0;Δ S > 0 |
| | B) | exothermic; ΔH < 0;Δ S > 0 |
| | C) | endothermic; ΔH < 0;Δ S < 0 |
| | D) | endothermic; ΔH < 0;Δ S > 0 |
| | E) | exothermic; ΔH > 0;Δ S < 0 |
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| 6 | |
Which of the following is true for a system at equilibrium? |
| | A) | ΔSsys = ΔSsurr |
| | B) | ΔSsys = -ΔSsurr |
| | C) | ΔSsys = ΔSsurr = 0 |
| | D) | ΔSuniv > 0 |
| | E) | ΔSsurr > ΔSsys
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| 7 | |
Consider the reaction
C9H20(l) + 14O2(g) →
9CO2(g) + 10H2O(g)
for which ΔGºf is -5848 kJ at 25º
C. Use this value and the following standard free energies of formation to calculate ΔGºf for liquid nonane, C9H20.
ΔGºf data (kJ/mol): O2(g), 0.0; CO2(g), -394.4; H2O(g), -228.6 |
| | A) | -610 kJ/mol |
| | B) | +610 kJ/mol |
| | C) | 12 kJ/mol |
| | D) | 635 kJ/mol |
| | E) | -635 kJ/mol |
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| 8 | |
Consider the following reactions and ΔGº values:
CaCO3(s) →
CaO(s) + CO2(g) ΔGº = + 130 kJ
3CaO(s) + 2H3PO4(aq) →
Ca3(PO4)2(s) + 3H2O(l) ΔGº = - 512 kJ
Calculate ΔGº for the reaction:
3CaCO3(s) + 2H3PO4(aq) →
Ca3(PO4)2(s) + 3CO2(g) + 3H2O(l) |
| | A) | -382 kJ |
| | B) | +382 kJ |
| | C) | -122 kJ |
| | D) | +122 kJ |
| | E) | -902 kJ |
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| 9 | |
A certain reaction has ΔHº = -14.2 kJ and ΔSº = +87.9 J/K. What is the value of ΔGº for this reaction? (Temperature is 25°C) |
| | A) | +40.4 kJ |
| | B) | -16.4 kJ |
| | C) | -26200 kJ |
| | D) | -40.4 kJ |
| | E) | -7820 kJ |
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| 10 | |
Predict the signs of ΔH°, ΔS°, and ΔG° for the vaporization of liquid water at 150°C. |
| | A) | ΔH° > 0, ΔS° > 0, ΔG° > 0 |
| | B) | ΔH° < 0, ΔS° < 0, ΔG° < 0 |
| | C) | ΔH° > 0, ΔS° < 0, ΔG° > 0 |
| | D) | ΔH° > 0, ΔS° > 0, ΔG° < 0 |
| | E) | none of the above |
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| 11 | |
Hydrogen sulfide decomposes according to the following reaction:
2H2S(g) →
2H2(g) + S2(g)
For this reaction at 298 K, ΔS° = 78.1 J/K, ΔH° = 169.4 kJ, and ΔG° = 146.1 kJ.
Calculate the value of ΔG° at a temperature of 700. K. |
| | A) | 41 kJ |
| | B) | 83 kJ |
| | C) | 115 kJ |
| | D) | 143 kJ |
| | E) | none of the above |
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| 12 | |
Sodium carbonate can be made by heating sodium hydrogen carbonate:
2NaHCO3(s) →
Na2CO3(s) + CO2(g) + H2O(g)
For this reaction, ΔH° = 128.9 kJ and ΔS° = 321 J/K. At approximately what temperature will K = 1? |
| | A) | 401.6 K |
| | B) | 401.6°C |
| | C) | 33.1 K |
| | D) | 33.1°C |
| | E) | none of the above |
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| 13 | |
A reaction has a value of ΔH = -249.6 kJ at 85°C. Above this temperature the reaction is spontaneous; below it, it is not spontaneous. Calculate ΔS at this temperature. |
| | A) | 697.2 J/K |
| | B) | 1434 J/K |
| | C) | -1434 J/K |
| | D) | -697.2 J/K |
| | E) | –2.936 x 103 J/K |
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| 14 | |
A reaction has an equilibrium constant Kc = 7.0 at 35°C. Calculate the value of ΔG° for the reaction. |
| | A) | -4.98 kJ |
| | B) | -2.46 kJ |
| | C) | -5.66 kJ |
| | D) | -2.16 kJ |
| | E) | none of the above |
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| 15 | |
For a system at equilibrium, ΔG is _____. |
| | A) | positive |
| | B) | negative |
| | C) | zero |
| | D) | equal to ΔH |
| | E) | equal to -TΔS |
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