- For a process at constant pressure, the heat absorbed or released is equal to:
a) Change in internal energy
b) Change in enthalpy
c) Change in entropy
d) Change in Gibbs free energy
Answer: b) Change in enthalpy
Explanation: At constant pressure, the heat absorbed or released by the system is equal to the change in enthalpy (ΔH).
- A reaction that absorbs heat from the surroundings has a:
a) Positive ΔG
b) Negative ΔS
c) Positive ΔH
d) Negative ΔH
Answer: c) Positive ΔH
Explanation: A reaction that absorbs heat from the surroundings is endothermic, and thus the enthalpy change (ΔH) is positive.
- If ΔH < 0 and ΔS > 0, a process will be:
a) Non-spontaneous at all temperatures
b) Spontaneous at all temperatures
c) Spontaneous at low temperatures only
d) Spontaneous at high temperatures only
Answer: b) Spontaneous at all temperatures
Explanation: When ΔH is negative and ΔS is positive, ΔG will be negative at all temperatures, indicating the process is spontaneous at all temperatures.
- The standard Gibbs free energy change (ΔG°) of a reaction is negative, which means:
a) The reaction is at equilibrium
b) The reaction is spontaneous under standard conditions
c) The reaction is non-spontaneous under standard conditions
d) The reaction is slow
Answer: b) The reaction is spontaneous under standard conditions
Explanation: A negative standard Gibbs free energy change indicates that the reaction is spontaneous under standard conditions.
- Which of the following is true for an irreversible process?
a) Entropy of the system decreases
b) Entropy of the system remains constant
c) Entropy of the universe increases
d) Entropy of the universe decreases
Answer: c) Entropy of the universe increases
Explanation: In an irreversible process, the entropy of the universe always increases according to the second law of thermodynamics.
- The entropy of a perfectly crystalline substance at absolute zero is:
a) Zero
b) Infinite
c) Negative
d) Positive
Answer: a) Zero
Explanation: According to the third law of thermodynamics, the entropy of a perfectly crystalline substance approaches zero as the temperature approaches absolute zero.
- Which condition would result in a non-spontaneous process?
a) ΔH < 0, ΔS < 0 at low temperatures b) ΔH > 0, ΔS > 0 at high temperatures
c) ΔH > 0, ΔS < 0 at all temperatures d) ΔH < 0, ΔS > 0 at high temperatures
Answer: c) ΔH > 0, ΔS < 0 at all temperatures
Explanation: A positive ΔH (endothermic process) and negative ΔS (decreasing entropy) will result in a positive ΔG at all temperatures, making the process non-spontaneous.
- If ΔG = 0 for a process, it means that:
a) The process is spontaneous
b) The process is non-spontaneous
c) The system is at equilibrium
d) The process is impossible
Answer: c) The system is at equilibrium
Explanation: A ΔG of zero indicates that the system is at equilibrium, meaning there is no net change in the system.
- Which of the following statements about Gibbs free energy is correct?
a) It is always negative for non-spontaneous reactions
b) It is positive for spontaneous reactions
c) It is the maximum amount of useful work obtainable from a process
d) It is the total energy of the system
Answer: c) It is the maximum amount of useful work obtainable from a process
Explanation: Gibbs free energy represents the maximum amount of useful work that can be obtained from a process at constant temperature and pressure.
- Which of the following reactions has an increase in entropy?
a) 2H₂(g) + O₂(g) → 2H₂O(l)
b) CaCO₃(s) → CaO(s) + CO₂(g)
c) 2SO₂(g) + O₂(g) → 2SO₃(g)
d) N₂(g) + 3H₂(g) → 2NH₃(g)
Answer: b) CaCO₃(s) → CaO(s) + CO₂(g)
Explanation: The decomposition of calcium carbonate produces a gas (CO₂), which increases the disorder of the system, hence increasing entropy.
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