Which of these has the highest standard molar entropy at 298 K and 1 atm pressure?
carbon dioxide, CO2
copper, Cu
ethanol, C2H5OH
hydrogen, H2
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Which of these has the highest standard molar entropy at 298 K and 1 atm pressure?
carbon dioxide, CO2
copper, Cu
ethanol, C2H5OH
hydrogen, H2
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Which of these gases would have the greatest standard molar entropy?
NH3
H2
N2
SO2
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What is the standard entropy change of the system, in J K–1 mol–1, for the reaction between nitrogen and hydrogen to form ammonia?
N2 + 3H2 → 2NH3
Standard molar entropy / J K–1 mol–1 | |
H2 | 130.6 |
N2 | 191.6 |
NH3 | 192.3 |
–198.8
–129.9
+129.9
+198.8
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The entropy change of the surroundings, ΔSsurroundings, and the entropy change of the system, ΔSsystem, for four different reactions are given.
Reaction | ΔSsurroundings / J K−1 mol−1 | ΔSsystem / J K−1 mol−1 |
P | +245 | +34 |
Q | +350 | −276 |
R | −482 | +65 |
S | −563 | −128 |
Which of these is thermodynamically feasible?
reaction P only
reactions P and Q only
reaction R only
reactions R and S only
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Ammonium nitrate is very soluble in water.
NH4NO3 (s) + aq → N (aq) + N (aq) ∆= +25.8 kJ mol−1
What is the best explanation for this?
all ammonium salts are soluble in water
the activation energy of the reaction is very low
the enthalpies of hydration of the ions are very exothermic
the entropy change of the system, ∆Ssystem , is positive
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The decomposition of calcium carbonate is an important reaction in the manufacture of cement.
CaCO3 (s) → CaO (s) + CO2 (g) ∆= +178 kJ mol−1
What are the signs of the entropy change of the system, ∆Ssystem , and of the entropy change of the surroundings, ∆Ssurroundings ?
Sign of ∆Ssystem | Sign of ∆Ssurroundings | |||
☐ | A | positive | positive | |
☐ | B | positive | negative | |
☐ | C | negative | positive | |
☐ | D | negative | negative |
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The standard molar entropy, , of a substance
is not affected by changes of state or changes in temperature
only changes when the temperature changes
only changes when the substance changes state
changes when the temperature changes and when the substance changes state
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The standard enthalpy change of solution of potassium chloride, KCl, is +17 kJ mol−1.
The solubility of potassium chloride in water at 298 K is 359 g dm−3.
Which of these explains the solubility of potassium chloride in water?
the hydration enthalpy of K+ and the lattice energy of KCl are exothermic
the hydration enthalpy of K+ and the lattice energy of KCl are endothermic
the total entropy change when KCl dissolves is positive
the total entropy change when KCl dissolves is negative
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