11 markeasy
Which of these has the highest standard molar entropy at 298 K and 1 atm pressure?
Choose your answer
carbon dioxide, CO2
copper, Cu
ethanol, C2H5OH
hydrogen, H2
Chemistry
9 questions · 10 marks · ≈ 10 min
Which of these has the highest standard molar entropy at 298 K and 1 atm pressure?
Choose your answer
carbon dioxide, CO2
copper, Cu
ethanol, C2H5OH
hydrogen, H2
Which of these gases would have the greatest standard molar entropy?
Choose your answer
NH3
H2
N2
SO2
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–1mol–1 | |
|---|---|
| H2 | 130.6 |
| N2 | 191.6 |
| NH3 | 192.3 |
Choose your answer
–198.8
–129.9
+129.9
+198.8
The entropy change of the surroundings, ΔSsurroundings, and the entropy change of the system, ΔSsystem, for four different reactions are given.
| Reaction | ΔS surroundings / J K−1 mol −1 ** | ΔS**system / J K−1mol−1 |
|---|---|---|
| P | +245 | +34 |
| Q | +350 | −276 |
| R | −482 | +65 |
| S | −563 | −128 |
Which of these is thermodynamically feasible?
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reaction P only
reactions P and Q only
reaction R only
reactions R and S only
Ammonium nitrate is very soluble in water.
NH4NO3 (s) + aq → N (aq) + N (aq) ∆H ^ ⦵= +25.8 kJ mol−1
What is the best explanation for this?
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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
The decomposition of calcium carbonate is an important reaction in the manufacture of cement.
CaCO3 (s) → CaO (s) + CO2 (g) ∆H ^ ⦵= +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 |
Choose your answer
The standard molar entropy, S ^ ⦵, of a substance
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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
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?
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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
Methane reacts with steam in the industrial process known as steam reforming. This is the main route for producing hydrogen used in the Haber process.
CH4 (g) + H2O (g) ⇌ CO (g) + 3H2 (g) ΔHθ = +206 kJ mol⁻¹
What are the signs of the entropy changes for this reaction?
| ΔSsystem | ΔSsurroundings | |
|---|---|---|
| A | negative | negative |
| B | negative | positive |
| C | positive | negative |
| D | positive | positive |
Choose your answer
From the equation in part (a), at which temperature(s) is the reaction feasible?
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At all temperatures
Never feasible
Only at high temperatures
Only at low temperatures