- Which of the following processes is endothermic?
a) Combustion of methane
b) Melting of ice
c) Freezing of water
d) Condensation of steam
Answer: b) Melting of ice
Explanation: An endothermic process absorbs heat from the surroundings. In the melting of ice, heat is absorbed to convert solid ice into liquid water.
- Entropy is a measure of:
a) Energy stored in a system
b) Heat content of a system
c) Disorder or randomness in a system
d) Work done by a system
Answer: c) Disorder or randomness in a system
Explanation: Entropy (S) measures the randomness or disorder of the particles in a system. Higher entropy indicates greater disorder.
- Which of the following is true for a spontaneous process?
a) ΔG > 0
b) ΔG = 0
c) ΔG < 0
d) ΔH = 0
Answer: c) ΔG < 0
Explanation: A process is spontaneous if the Gibbs free energy (ΔG) is negative. This indicates that the process can occur without external energy input.
- For an exothermic reaction, which of the following is true?
a) ΔH > 0
b) ΔH = 0
c) ΔH < 0
d) ΔS < 0
Answer: c) ΔH < 0
Explanation: In an exothermic reaction, heat is released into the surroundings, which means the change in enthalpy (ΔH) is negative.
- The unit of enthalpy change (ΔH) is:
a) Joule (J)
b) Kilocalorie (kcal)
c) Joule per mole (J/mol)
d) Calorie (cal)
Answer: c) Joule per mole (J/mol)
Explanation: Enthalpy change is the heat change per mole during a process and is measured in Joules per mole (J/mol).
- For which process is the entropy change positive?
a) Freezing of water
b) Condensation of steam
c) Sublimation of dry ice
d) Deposition of iodine
Answer: c) Sublimation of dry ice
Explanation: Sublimation involves a solid directly converting into gas, which increases the disorder of the system, hence increasing entropy.
- What happens to the Gibbs free energy of a system at equilibrium?
a) ΔG > 0
b) ΔG = 0
c) ΔG < 0
d) None of the above
Answer: b) ΔG = 0
Explanation: At equilibrium, the Gibbs free energy change (ΔG) is zero because there is no net change occurring in the system.
- Which of the following conditions favors a spontaneous reaction at all temperatures?
a) ΔH > 0, ΔS > 0
b) ΔH < 0, ΔS > 0
c) ΔH > 0, ΔS < 0 d) ΔH < 0, ΔS < 0 Answer: b) ΔH < 0, ΔS > 0
Explanation: A negative ΔH (exothermic) and a positive ΔS (increasing disorder) always favor spontaneity, regardless of temperature.
- The entropy of a perfectly crystalline substance at absolute zero is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: c) Zero
Explanation: According to the third law of thermodynamics, the entropy of a perfect crystal at absolute zero is exactly zero because there is no randomness or disorder in the arrangement of particles.
- Which of the following processes decreases entropy?
a) Evaporation of water
b) Mixing of gases
c) Freezing of water
d) Dissolution of salt in water
Answer: c) Freezing of water
Explanation: In the freezing process, water molecules become more ordered as they arrange into a solid structure, which decreases entropy.
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