Use the following information to answer questions 1-5:
Reaction 1: N₂H₄(l) + H₂(g) → 2 NH₃(g) ΔH = ?
Reaction 2: N₂H₄(l) + CH₄O(l) → CH₂O(g) + N₂(g) + 3 H₂(g) ΔH = -37 kJ/molₑ
Reaction 3: N₂(g) + 3 H₂(g) → 2 NH₃(g) ΔH = -46 kJ/molₑ
Reaction 4: CH₂O(l) → CH₄O(g) + H₂(g) ΔH = -65 kJ/molₑ
1. What is the enthalpy change for reaction 1?
- (A) -148 kJ/molrxn
- (B) -56 kJ/molrxn
- (C) -18 kJ/molrxn
- (D) +148 kJ/molrxn
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Correct Answer: (A) -148 kJ/molₑ2. If reaction 2 were repeated at a higher temperature, how would the reaction’s value for ΔG be affected?
- (A) It would become more negative because entropy is a driving force behind this reaction.
- (B) It would become more positive because the reactant molecules would collide more often.
- (C) It would become more negative because the gases will be at a higher pressure.
- (D) It will stay the same; temperature does not affect the value for ΔG.
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Correct Answer: (A)3. Under what conditions would reaction 3 be thermodynamically favored?
- (A) It is always favored.
- (B) It is never favored.
- (C) It is only favored at low temperatures.
- (D) It is only favored at high temperatures.
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Correct Answer: (C)4. If 64 g of CH₄O were to decompose via reaction 4, approximately how much energy would be released or absorbed?
- (A) 65 kJ of energy will be absorbed.
- (B) 65 kJ of energy will be released.
- (C) 130 kJ of energy will be absorbed.
- (D) 130 kJ of energy will be released.
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Correct Answer: (D)5. A 2.0 L flask holds 0.40 g of helium gas. If the helium is evacuated into a larger container while the temperature is held constant, what will the effect on the entropy of the helium be?
- (A) It will remain constant because the number of helium molecules does not change.
- (B) It will decrease because the gas will be more ordered in the larger flask.
- (C) It will decrease because the molecules will collide with the sides of the larger flask less often than they did in the smaller flask.
- (D) It will increase because the gas molecules will be more dispersed in the larger flask.
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Correct Answer: (D)6. 2 Al(s) + 3 Cl₂(g) → 2 AlCl₃(s)
The reaction above is not thermodynamically favored under standard conditions, but it becomes thermodynamically favored as the temperature decreases toward absolute zero. Which of the following is true at standard conditions?
- (A) ΔS and ΔH are both negative.
- (B) ΔS and ΔH are both positive.
- (C) ΔS is negative, and ΔH is positive.
- (D) ΔS is positive, and ΔH is negative.
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Correct Answer: (A)7. SF₄(g) + H₂O(l) → SO₂(g) + 4 HF(g) ΔH = -828 kJ/mol
Which of the following statements accurately describes the above reaction?
- (A) The entropy of the reactants exceeds that of the products.
- (B) H₂O(l) will always be the limiting reagent.
- (C) This reaction is never thermodynamically favored.
- (D) The temperature of the surroundings will increase as this reaction progresses.
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Correct Answer: (D)8. H₂O(l) → H₂O(s)
Which of the following is true for this process at STP?
- (A) The value for ΔS is positive.
- (B) The value for ΔG is zero.
- (C) The value for ΔH is positive.
- (D) The reaction is favored.
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Correct Answer: (D)9. In which of the following reactions is entropy increasing?
- (A) 2 SO₃(g) → 2 SO₂(g) + O₂(g)
- (B) CO₂(g) + H₂O(g) → H₂(g) + CO₂(g)
- (C) H₂(g) + Cl₂(g) → 2 HCl(g)
- (D) 2 NO₂(g) → 2 NO(g) + O₂(g)
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Correct Answer: (A)Question 10:
The reaction shown in the diagram below is accompanied by a large increase in temperature. If all molecules shown are in their gaseous state, which statement accurately describes the reaction?
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Options:
- (A) It is an exothermic reaction in which entropy increases.
- (B) It is an exothermic reaction in which entropy decreases.
- (C) It is an endothermic reaction in which entropy increases.
- (D) It is an endothermic reaction in which entropy decreases.
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Correct Answer: (A)Question 11:
In which of the following circumstances is the value for \( K_{eq} \) always greater than 1?
Options:
- (A) \( \Delta H \) is Positive, \( \Delta S \) is Positive
- (B) \( \Delta H \) is Positive, \( \Delta S \) is Negative
- (C) \( \Delta H \) is Negative, \( \Delta S \) is Negative
- (D) \( \Delta H \) is Negative, \( \Delta S \) is Positive
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Correct Answer: (D)
Question 12:
Which expression below should be used to calculate the mass of copper that can be plated out of a 1.0 M Cu(NO₃)₂ solution using a current of 0.75 A for 5.0 minutes?
Options:
- (A) \(\dfrac{(5.0)(60)(0.75)(63.55)}{(96,500)(2)}\)
- (B) \(\dfrac{(5.0)(60)(63.55)(2)}{(0.75)(96,500)}\)
- (C) \(\dfrac{(5.0)(60)(96,500)(0.75)}{(63.55)(2)}\)
- (D) \(\dfrac{(5.0)(60)(96,500)(63.55)}{(0.75)(2)}\)
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Correct Answer: (A)
Question 13:
What is the general relationship between temperature and entropy for diatomic gases?
Options:
- (A) They are completely independent of each other; temperature has no effect on entropy.
- (B) There is a direct relationship, because at higher temperatures there is an increase in energy dispersal.
- (C) There is an inverse relationship, because at higher temperatures substances are more likely to be in a gaseous state.
- (D) It depends on the specific gas and the strength of the intermolecular forces between individual molecules.
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Correct Answer: (B)
Question 14:
A strip of metal X is placed into a solution containing Y²⁺ ions and no reaction occurs. When metal X is placed in a separate solution containing Z²⁺ ions, metal Z starts to form on the strip. Which of the following choices organizes the reduction potentials for these cations from greatest to least?
Options:
- (A) \( X^{2+} > Y^{2+} > Z^{2+} \)
- (B) \( Y^{2+} > Z^{2+} > X^{2+} \)
- (C) \( Z^{2+} > X^{2+} > Y^{2+} \)
- (D) \( Y^{2+} > X^{2+} > Z^{2+} \)
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Correct Answer: (B)
Use the following information to answer questions 15–17:
Pennies are made primarily of zinc, which is coated with a thin layer of copper through electroplating, using a setup like the one shown below. The solution in the beaker is a strong acid (which produces H⁺ ions), and the cell is wired so that the copper electrode is the anode and the zinc penny is the cathode.
Diagram: A beaker contains Zn and Cu electrodes connected to a battery. The solution includes H⁺ ions.
| Half-Reaction | Standard Reduction Potential (V) |
|---|---|
| Cu²⁺ + 2 e⁻ → Cu(s) | +0.34 V |
| 2 H⁺ + 2 e⁻ → H₂(g) | 0.00 V |
| Ni²⁺ + 2 e⁻ → Ni(s) | -0.25 V |
| Zn²⁺ + 2 e⁻ → Zn(s) | -0.76 V |
Question 15:
When the cell is connected, which of the following reactions takes place at the anode?
Options:
- (A) Cu²⁺ + 2 e⁻ → Cu(s)
- (B) Cu(s) → Cu²⁺ + 2 e⁻
- (C) 2 H⁺ + 2 e⁻ → H₂(g)
- (D) H₂(g) → 2 H⁺ + 2 e⁻
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Correct Answer: (B)
Question 16:
What is the required voltage to make this cell function?
Options:
- (A) 0.34 V
- (B) 0.42 V
- (C) 0.76 V
- (D) 1.10 V
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Correct Answer: (D)
Question 17:
If, instead of copper, a nickel bar were to be used, could nickel be plated onto the zinc penny effectively? Why or why not?
Options:
- (A) Yes, the SRP of Ni²⁺ is greater than that of Zn²⁺, which is all that is required for Ni²⁺ to be reduced at the cathode.
- (B) Yes, Ni²⁺ is able to take electrons from the H⁺ ions in solution, allowing it to be reduced.
- (C) No, the SRP of Ni²⁺ is lower than that of H⁺ ions, which means the only product being produced at the cathode would be hydrogen gas.
- (D) No, the SRP of Ni²⁺ is negative, meaning it cannot be reduced in an electrolytic cell.
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Correct Answer: (C)
Use the following information to answer questions 18–22:
Two half-cells are set up as follows:
- Half-Cell A: Strip of Cu(s) in CuNO3(aq)
- Half-Cell B: Strip of Zn(s) in Zn(NO3)2(aq)
When the cells are connected according to the diagram below, the following reaction occurs:
2 Cu+(aq) + Zn(s) → 2 Cu(s) + Zn2+(aq) (Eo = +1.28 V)
Question 18:
Correctly identify the anode and cathode in this reaction as well as where oxidation and reduction are taking place.
Options:
- (A) Cu is the anode where oxidation occurs, and Zn is the cathode where reduction occurs.
- (B) Cu is the anode where reduction occurs, and Zn is the cathode where oxidation occurs.
- (C) Zn is the anode where oxidation occurs, and Cu is the cathode where reduction occurs.
- (D) Zn is the anode where reduction occurs, and Cu is the cathode where oxidation occurs.
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Correct Answer: (C)
Question 19:
How many moles of electrons must be transferred to create 127 g of copper?
Options:
- (A) 1 mole of electrons
- (B) 2 moles of electrons
- (C) 3 moles of electrons
- (D) 4 moles of electrons
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Correct Answer: (B)
Question 20:
If the Cu2+ + e- → Cu(s) half-reaction has a standard reduction potential of +0.52 V, what is the standard reduction potential for the Zn2+ + 2 e- → Zn(s) half-reaction?
Options:
- (A) +0.76 V
- (B) -0.76 V
- (C) +0.24 V
- (D) -0.24 V
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Correct Answer: (B)
Question 21:
As the reaction progresses, what will happen to the overall voltage of the cell?
Options:
- (A) It will increase as [Zn2+] increases.
- (B) It will increase as [Cu+] increases.
- (C) It will decrease as [Zn2+] increases.
- (D) The voltage will remain constant.
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Correct Answer: (C)
Question 22:
What will happen in the salt bridge as the reaction progresses?
Options:
- (A) The Na+ ions will flow to the Cu/Cu+ half-cell.
- (B) The Br- ions will flow to the Cu/Cu+ half-cell.
- (C) Electrons will transfer from the Cu/Cu+ half-cell to the Zn/Zn2+ half-cell.
- (D) Electrons will transfer from the Zn/Zn2+ half-cell to the Cu/Cu+ half-cell.
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Correct Answer: (A)