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Entropy quiz #2

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Terms in this set (10)

  • What type of substance has the largest standard molar entropy, S° (298.15 K)?
    A complex, heavy gas at 298.15 K has the largest standard molar entropy.
  • An object at 20°C absorbs 25.0 J of heat. What is the change in entropy ΔS of the object?
    ΔS = q/T; T = 293 K, so ΔS = 25.0 J / 293 K ≈ 0.085 J/K.
  • Given ΔS_sys equals 412 J/K and ΔS_univ equals -186 J/K, what is ΔS_surr?
    ΔS_surr = ΔS_univ - ΔS_sys = -186 J/K - 412 J/K = -598 J/K.
  • What type of substance has the smallest standard molar entropy, S° (298.15 K)?
    A simple, light solid at 298.15 K has the smallest standard molar entropy.
  • Predict the sign of the entropy change, ΔS°, for each of the reactions displayed.
    Reactions producing more disorder (more gas, more particles) have positive ΔS°; those producing more order have negative ΔS°.
  • Classify each process by its individual effect on the entropy of the universe, S.
    Spontaneous processes increase the entropy of the universe; non-spontaneous processes decrease it.
  • A negative change in entropy indicates that
    A negative change in entropy indicates the system is becoming more ordered.
  • Choose the compound with the largest standard molar entropy, S° (298.15 K).
    The compound that is a complex, heavy gas at 298.15 K will have the largest standard molar entropy.
  • According to the third law of thermodynamics, what is the entropy of a substance at absolute zero (0 K)?
    At absolute zero (0 K), the entropy of a substance is zero because all molecular motion stops and there is perfect order.
  • What is Troughton's rule and when is it typically applied in entropy calculations?
    Troughton's rule states that the entropy of vaporization for many substances is about 88 J/(mol·K) when one mole of liquid is converted to gas at its normal boiling point; it is used to estimate entropy changes during vaporization.