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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 0º
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 25º
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) | 401.6º
C |
| | C) | 33.1 K |
| | D) | 33.1º
C |
| | E) | none of the above |
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13 | |
A reaction has a value of ΔH = -249.6 kJ at 85º
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 35º
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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