Chemistry questions help
1. If 4.168 kJ of heat is added to a calorimeter containing 75.40 g of water, the temperature of the water and the calorimeter increases from 24.58°C to 35.82°C. Calculate the heat capacity of the calorimeter (in J/°C). The specific heat of water is 4.184 J/g•°C.
a. | 622 J/°C |
b. | 55.34 J/°C |
c. | 315.5 J/°C |
d. | 25.31 J/°C |
e. | 17.36 J/°C |
2. How much heat is absorbed in the complete reaction of 3.00 grams of SiO2 with excess carbon in the reaction below? DH0 for the reaction is +624.6 kJ.
SiO2(g) + 3C(s) ®SiC(s) + 2CO(g)
a. | 366 kJ |
b. | 1.13 ´ 105 kJ |
c. | 5.06 kJ |
d. | 1.33 ´ 104 kJ |
e. | 31.2 kJ |
3. How much heat is released when 75 g of octane is burned completely if the enthalpy of combustion is -5,500 kJ/mol C8H18?
C8H18 + 25/2 O2® 8CO2 + 9H2O
a. | 7200 kJ |
b. | 8360 kJ |
c. | 4.1 ´ 105 kJ |
d. | 3600 kJ |
e. | 5500 kJ |
4. The burning of 80.3 g of SiH4 at constant pressure gives off 3790 kJ of heat. Calculate DH for this reaction.
SiH4(g) + 2O2(g) ® SiO2(s) + 2H2O(l)
a. | -1520 kJ/molrxn |
b. | - 47.2 kJ/molrxn |
c. | - 4340 kJ/molrxn |
d. | -2430 kJ/molrxn |
e. | + 4340 kJ/molrxn |
5. Which of the following statements is incorrect?
a. | The thermochemical standard state of a substance is its most stable state under one atmosphere pressure and at some specific temperature (298 K if not specified) |
b. | A superscript zero, such as DH0, indicates a specified temperature of 0°C. |
c. | For a pure substance in the liquid or solid phase, the standard state is the pure liquid or solid. |
d. | For a pure gas, the standard state is the gas at a pressure of one atmosphere. |
e. | For a substance in solution, the standard state refers to one-molar concentration.
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6. For which of the following substances does = 0?
a. | CO2(g) |
b. | H2O(g) |
c. | Na(s) |
d. | Br2(g) |
e. | C(diamond) |
7. Calculate the amount of heat released in the complete combustion of 8.17 grams of Al to form Al2O3(s) at 25°C and 1 atm. DH for Al2O3(s) = 1676 kJ/mol
4Al(s) + 3O2(g) ® 2Al2O3(s)
a. | 254 kJ |
b. | 203 kJ |
c. | 127 kJ |
d. | 237 kJ |
e. | 101 kJ
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8. Which of the following is not a formation reaction?
a. | 1/2H2(g) + 1/2 Br2(l) ®HBr(g) |
b. | H2(g) + 1/2O2(g) ® H2O(l) |
c. | Ca(s) + 1/2O2(g) ®CaO(s) |
d. | 4Al(s) + 3/2O2(g) ® Al2O3(s) |
e. | H2O(l) + SO3(l) ® H2SO4(l) |
9. Given the standard heats of formation for the following compounds, calculate DHfor the following reaction.
| CH4(g) | + H2O(g) | ® | CH3OH(l) | + H2(g) |
DH | -75 | -242 |
| -238 | 0 |
a. | +79 kJ |
b. | -79 kJ |
c. | +594 kcal |
d. | -594 kcal |
e. | - 405 kJ
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10. Given the following at 25°C, calculate DHfor HPO3(s) at 25°C.
P4O10(s) + 4HNO3(l) ® 4HPO3(s) + N2O5(s) | DH |
DH= -2984 kJ/mol for P4O10(s), -174.1 kJ/mol for HNO3(l), and - 43.1 kJ/mol for N2O5(s).
a. | -528.0 kJ/mol |
b. | -1474 kJ/mol |
c. | -948.5 kJ/mol |
d. | +1474 kJ/mol |
e. | -954.5 kJ/mol
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11. How much heat is released when 6.38 grams of Ag(s) reacts by the equation shown below at standard state conditions?
4Ag(s) + 2H2S(g) + O2(g) ® 2Ag2S(s) + 2H2O(l)
Substance | |
Ag(s) | 0 |
H2S(g) | -20.6 |
O2(g) | 0 |
Ag2S(s) | -32.6 |
H2O(l) | -285.8 |
a. | 8.80 kJ |
b. | 69.9 kJ |
c. | 22.1 kJ |
d. | 90.8 kJ |
e. | 40.5 kJ
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12. Which of the following techniques cannot be used to calculate DHrxn?
a. | Calorimetry |
b. | Using melting points of reactants and products |
c. | Hess's Law |
d. | Using of Heats of Formation of reactants and products |
e. | Using bond energies of reactants and products
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13. Evaluate DH0 for the following reaction from the given bond energies.
2HBr(g) ® H2(g) + Br2(g)
DHH-H = 436 kJ/mol, DHBr-Br = 193 kJ/mol, DHH-Br = 366 kJ/mol
a. | -103 kJ |
b. | -143 kJ |
c. | +103 kJ |
d. | +142 kJ |
e. | 259 kJ
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14. A positive change in entropy represents:
a. | an increase in molecular disorder |
b. | release of thermal energy |
c. | a decrease in thermal energy |
d. | a process that is always spontaneous |
e. | a process that cannot occur spontaneously
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15. The second law of thermodynamics states:
a. | All exothermic processes also increase entropy. |
b. | The enthalpy of the universe always increases in spontaneous processes. |
c. | A spontaneous process always increases entropy. |
d. | DH<0 and DS >0 for all spontaneous processes |
e. | The entropy of the universe always increases in spontaneous processes.
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16. What is the entropy change of the reaction below at 298 K and 1 atm pressure?
| N2(g) | + 3H2(g) | ® | 2NH3(g) |
S | 191.5 | 130.6 |
| 192.3 |
a. | -198.7 J/K |
b. | 76.32 J/K |
c. | -129.7 J/K |
d. | 303.2 J/K |
e. | 384.7 J/K
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17. The heat of vaporization of methanol, CH3OH, is 35.20 kJ/mol. Its boiling point is 64.6°C. What is the change in entropy for the vaporization of methanol?
a. | -17.0 J/mol•K |
b. | 3.25 J/mol•K |
c. | 17.0 J/mol•K |
d. | 104 J/mol•K |
e. | 543 J/mol•K
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18. Which of the following statements regarding the third law of thermodynamics is incorrect?
a. | The absolute S is zero at 0 Kelvin. |
b. | The absolute S at 298 K can be positive or negative. |
c. | Pure substances have positive absolute S at T > 0 Kelvin. |
d. | Absolute zero gives a reference point for determining absolute S. |
e. | The absolute S is greater at 300 K than 100 K for a given substance.
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19. Which of following would have the highest value of absolute entropy per mole?
a. | water at 50°C |
b. | water at 10°C |
c. | ice at -10°C |
d. | 1 MNaCl at 50°C |
e. | 1 MNaCl at 10°C
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20. Based on the relationship of entropy to the degree of disorder in a system, which response includes all the following changes that represent an increase in entropy, and no others?
I. | the freezing of water |
II. | the condensation of steam |
III. | sublimation (vaporization) of dry ice, solid CO2 |
IV. | the extraction of salts and pure water from seawater |
a. | I and IV |
b. | II and IV |
c. | I, and II |
d. | III |
e. | I and III
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21. Which response includes all the following processes that are accompanied by an increase in entropy, and only those processes?
I. | boiling water |
II. | freezing water |
III. | N2(g) + 3H2(g) ® 2NH3(g) |
IV. | Br2(l) ® Br2(g) |
a. | I and II |
b. | III and IV |
c. | I and IV |
d. | II, III, and IV |
e. | another one or another combination
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22. Which of the following changes represent a decrease in entropy?
a. | Precipitation of CaCO3 to form a seashell |
b. | Evaporation of gasoline |
c. | Decomposition of a dead animal |
d. | Melting snow |
e. | Diffusion of perfume throughout a room.
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23. Consider the conversion of a substance from solid to liquid.
Solid Liquid
At one atmosphere pressure and at the melting point of the substance, __________.
a. | DH = 0 for the process |
b. | DS = 0 for the process |
c. | DE = 0 for the process |
d. | DG = 0 for the process |
e. | both DH = 0 and DE = 0 for the process
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24. Evaluate DG0 for the reaction below at 25°C.
| 2C2H2(g) | + 5O2(g) | ® | 4CO2(g) | + 2H2O(l) |
DG | 209.2 | 0 |
| -394.4 | -237.2 |
a. | -1409 kJ |
b. | -2599 kJ |
c. | -1643 kJ |
d. | -2470 kJ |
e. | -766 kJ
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51. Calculate DG0 at 298 K for the reaction below.
| Fe2O3(s) | + 13CO(g) | ® | 2Fe(CO)5(g) | + 3CO2(g) |
DH | -824.2 | -110.5 |
| -733.8 | -393.5 |
S0 (J/mol•K) | 87.4 | 197.6 |
| 445.2 | 213.6 |
a. | +63.6 kJ |
b. | +26.8 kJ |
c. | -243.1 kJ |
d. | -52.2 kJ |
e. | -193.3 kJ
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52. The standard molar enthalpy of formation of NO2(g) is 33.2 kJ/mol at 25°C and that of N2O4(g) is 9.16 kJ/mol. At 25°C their absolute entropies are 240.0 and 304.2 J/mol•K, respectively. Use the above data to calculate the standard Gibbs free energy change for the following reaction at 25°C. Express your answer in the form DG0 = __________ kJ.
N2O4(g) ® 2NO2(g)
a. | 4.1 kJ |
b. | 21.3 kJ |
c. | 4.8 kJ |
d. | 41.5 kJ |
e. | 11.4 kJ
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53. For which set of values of DH and DS will a reaction be spontaneous (product-favored) at all temperatures?
a. | DH = +10 kJ, DS = -5 J/K |
b. | DH = -10 kJ, DS = -5 J/K |
c. | DH = -10 kJ, DS = +5 J/K |
d. | DH = +10 kJ, DS = +5 J/K |
e. | no such values exist |
12 years ago
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